Tart Key Lime Bars
E
By Emma
Certified Culinary Professional
•
Recipe tested & approved
A zesty lime custard over a crunchy spiced cookie crust. The crust uses crushed Biscoff cookies for a caramel twist. The filling boasts bright lime juice and zest, balanced with egg yolks and sweetened condensed milk. Baked until just set, a slight wiggle remains at the center. Chilled thoroughly for clean slices. Topped with fluffy homemade whipped cream folded with sour cream and vanilla. A garnish of lime zest adds fresh aroma. Timing guided by texture and aroma more than clocks. A lively treat with layers of tang, sweet, and crunch. Substitute ginger snaps if needed or try graham crackers for a milder base. Slick, reliable, crowd-pleasing bars with a zingy finish.
Prep:
12 min
Cook:
27 min
Total:
Servings:
12 bars
#lime
#dessert
#American
#baking
#whipped cream
#cookies
#easy dessert
Started out with standard key lime pie attempts—watery, flavorless, crumbly. Switched cookie base midway to Biscoff for caramel snap and grit that holds shape. Crucial: zest first, then juice limes. You want that bright hit but slightly creamy body from yolks thickened properly. Whipping yolks takes patience; it’s the difference between sloppy filling and custardy punch. Baking: enough to set, not bake into cement. Jiggly center spells success. Chilling overnight fixes texture, tightens crust and filling. Whipped cream with sour cream surprise adds tang, cuts sweetness, holds better over time. Learned to trust senses over timers here. Try ginger snaps for barkier crust twist.
Ingredients
- 1 1/2 cups Biscoff cookies or ginger snaps, crushed
- 6 tbsp unsalted butter, melted
- 4 large egg yolks
- 3 tbsp lime zest
- 1 can (14 oz) sweetened condensed milk
- 1/3 cup freshly squeezed lime juice
- Pinch kosher salt
- 1 1/4 cups heavy cream
- 1 1/2 tbsp powdered sugar
- 1 tsp vanilla extract
- 2 tsp sour cream
About the ingredients
Cookie crust critical—Biscoff’s caramel warmth punches through tart lime. No processor? No problem; manual crushing works, just takes elbow grease. Butter needs to be fully melted but cool enough not to melt cookie fats before baking. Egg yolks: fresh and at room temp whip better, so plan ahead. Limes: fresh zest and juice bring brightness; bottled won’t cut it. Sweetened condensed milk is thick, sweet glue for custard; don’t swap for evaporated milk or canned cream. Heavy cream whipped with sour cream less likely to break or turn grainy. Powdered sugar quantity adjustable to taste and cream stability. Vanilla binds whipped cream flavor but vanilla extract (natural) preferred over imitation.
Method
- Heat oven to 355 F. Line 8x8 pan with parchment loosely hanging over edges for easy removal.
- Crush cookies fine but not powdery. Best in food processor. No processor? Bag cookies and crush with rolling pin or skillet with force.
- Drizzle melted butter over crumbs. Pulse or mix until mix looks sandy but sticks slightly when pressed.
- Press firmly into pan’s bottom evenly. I use a flat-bottomed glass. Press hard enough so crumbs hold but don’t over compact or it gets rock hard.
- Bake crust for 11 minutes. Tiny scent of caramel fills air. Watch edges just a bit darker. Remove, let cool while prepping filling.
- Zest first, in long curls for garnish later. Juice limes freshly - bottled juice dulls zing and throws off balance.
- Whisk yolks and zest on high with mixer whisk attachment until mixture thickens like light hollandaise, about 3-4 mins. Don’t rush or it won’t whip up.
- Add condensed milk gradually. Whip in at high speed until filling gains body and volume, roughly 2-3 minutes. Texture is creamy, slightly glossy.
- Mixer off. Stir in lime juice and a pinch salt with spatula. Fold gently but thoroughly. Scrape down sides - zest bits cling to whisk; don’t waste those.
- Pour filling onto crust. Smooth surface with offset spatula or back of spoon. Should spread easily; if too loose, a quick extra mix needed.
- Bake 12-17 minutes. Center should jiggle slightly, not fully set. Edges firm, center creamy. Avoid overbake; cracks mean dryness.
- Cool bars to room temp before chilling. Cold helps filling set without cracking, develop clean lime flavor.
- Chill minimum 3 hours or overnight if patient. Bars get firmer, easier to cut into neat squares.
- Whip heavy cream at medium-high speed until soft peaks form, 1-3 minutes depending on mixer strength.
- Add powdered sugar, vanilla, sour cream. Beat until medium peaks, smooth but holds shape. Sour cream adds tangy depth, stops whipped cream from overly sweet cloying.
- Adjust sugar to taste; powdered sugar quantity flexible based on cream sweetness preference.
- Spread whipped cream over chilled bars evenly. Return to fridge 30 minutes to firm topping. Zest sprinkle on top for aroma, zing, pop of color.
- Remove bars with parchment edges, slice with sharp knife warmed in hot water for cleaner edges. Wipe blade between cuts.
- Serve cold. Bars hold for 3 days refrigerated, but loses firmness if left out long.
Cooking tips
Line pan carefully but loosely for easy bar removal—prepping early saves headaches. Crust: pressing with firm glass ensures base holds but doesn’t press rock hard—textural balance is key. Baking time guesses vary—watch visual cues: crust edges darken, filling edges firm. Whisk yolks first to create emulsified base that traps air; skip this and filling might separate or stay runny. Folding in lime juice last preserves volume; interrupted mixing breaks emulsion. Cool filling completely before chilling. Whipped cream: start slow, then medium speed prevents overshooting soft peaks; incorporate sour cream at medium peaks stage to avoid deflation. Chill assembled bars to firm topping before slicing. Use sharp, warm knife wiped after each slice to keep bars clean and pretty. Refrigerate leftovers tightly wrapped.
Chef's notes
- 💡 Cookies crushed but not powdery. If food processor fails, heavy rolling pin or skillet with force. Texture matters. Butter fully melted but not hot or will melt fats prematurely. Press crumbs evenly - flat glass best. Press too hard and crust is rock hard; too soft and it falls apart. Test by pressing crumbs between fingers before baking.
- 💡 Zest first then juice limes. Bottled lime juice dulls brightness—skip if fresh limes around. Whisk yolks and zest at high speed until mixture thickens, think light hollandaise, 3-4 mins. Slow here kills volume. Add condensed milk slow - whipping creates airy filling that won’t separate. Stop mixer carefully to fold juice gently preserving whip.
- 💡 Bake crust 11 minutes only. Watch edge color to avoid bitter burnt caramel notes. Filling baking 12-17 mins - center jiggles slightly like lightly set custard. Edges firm but watch doneness to prevent cracks. Remove early rather than overdone, bars continue firming when cooled. Oven temps vary, sensory cues over timers.
- 💡 Chill bars minimum 3 hours or overnight. Texture tightens, edges sharpen. Room temperature cooling before fridge prevents cracking. Whipped cream: soft peaks formed at medium-high speed. Add powdered sugar and sour cream once soft peaks form. Sour cream adds tang and stability, prevents grainy or overly sweet whipped cream - don’t skip.
- 💡 Use parchment edges to lift bars for neat removal. Slice bars with knife warmed in hot water then wiped clean between cuts for sharp clean edges. Zest curls sprinkled last step add aroma and texture contrast. Substitute ginger snaps if Biscoff unavailable for barkier crust flavor or graham crackers for milder base but affect moisture absorption.
Common questions
Can I swap Biscoff for other cookies?
Yes. Ginger snaps add barkier crunch, more spice. Graham crackers milder, less caramel notes. Adjust butter slightly if dry cookies. Crushing method stays same; processor or manual fine.
How do I know when custard filling is done?
Jiggle test. Center should wiggle slightly, not fully firm. Edges start to set. Overbake and cracks form, dryness follows. Oven temp varies, so watch edges color and feel for subtle jiggle.
What if my whipped cream breaks or gets grainy?
Usually whipped too fast or overwhipped. Add sour cream mid-whip to smooth, add tang and help stabilize. Powdered sugar type matters - coarse sugar won’t dissolve well. Chill bowl and beaters help keep cream cold, less risk of breaking.
How long to store and how?
Fridge best, bars last 3 days max. Wrap tight to avoid drying or absorbing fridge odors. Can freeze but texture changes, best thawed gently overnight chilled. Avoid room temp storage to maintain firm topping and crisp crust.
