Preheat your oven to 350°F (175°C). Line an 11x7 inch baking pan with parchment paper.

Crush the Biscoff cookies and graham crackers in a food processor until they form fine crumbs. Stream in the melted butter and pulse until combined. The mixture should look coarse and sandy.

If you don't have a food processor, place the cookies in an airtight bag and crush them using a rolling pin or heavy-bottomed skillet.

Pour the crumb mixture into the prepared pan and press it into an even layer using a flat-bottomed glass or measuring cup.

Bake the crust for 10 minutes. Remove from the oven and set aside to cool.

Zest and juice the limes.

Using an electric mixer with the whisk attachment, beat the egg yolks and lime zest on high speed for 2-3 minutes until slightly thickened.

Add the sweetened condensed milk and beat on high speed for 1-2 minutes until thick and voluminous.

Turn off the mixer and add the lime juice and a pinch of salt. Stir with a rubber spatula until combined, making sure to incorporate any zest stuck to the whisk.

Pour the filling over the crust and smooth the top.

Bake for 10-15 minutes until the center is mostly set but still slightly jiggly.

Remove from the oven and let cool to room temperature, then refrigerate for at least 3 hours or overnight.

Using a mixer, beat the mascarpone cheese, and powdered sugar for 30 seconds, or just until creamy. Pour in the heavy cream, and start the mixer on low and beat until combined. Slowly increase the speed and beat until stiff peaks, be careful not to overmix or the mixture will curdle. Add lime zest for garnish.

Spread the whipped cream over the chilled key lime pie bars in an even layer.

Refrigerate for an additional 30 minutes before slicing.

Garnish with more lime zest and enjoy!