Imagine a puckery key lime custard offset by the spicy sweetness of Belgian speculoos cookies. Top that with fresh native blueberries bound in a shiny glaze. Those ideas, along with a new rectangular tart pan, inspired this Blueberry Key Lime Tart Biscoff Crust. It is the perfect picnic dessert. Its flavors embody summer. The tart travels well, cuts into uniform slices, and is tangy and delicious.
For many years, I made a blueberry tart out of cheesecake batter baked in a shallow graham cracker crust. When I found key limes at the store, I knew it was time to make a custardy key lime pie. But I couldn’t ignore the bounty of fresh blueberries this season. Because the tartness of lime complements blueberries, I felt the key lime could take a supporting role as a filling under a thick blanket of the fruit.
To keep the blueberries from rolling off the tart onto the floor, I used an old trick: binding the berries in preserves. It allows me to pile on the fruit without fear that more blueberries will land on the floor than on your plate.
Because of their high fat and sugar content, Biscoff cookies soften easily. (Biscoff are a type of Belgian spice cookies called speculoos. They are crisp, intensly dark and sweet.) Crust made with them starts to weep within 24 hours of being filled. However, you can make the crust a day or two ahead. Alternatively, you can swap graham cracker crumbs for the ground Biscoff cookies if you like. The crust will hold up longer, allowing you to bake and fill the tart a day ahead.
Jump to Recipe
Pressing the buttery ground Biscoff cookie crumbs firmly makes for a solid crust.
Pinch the edges of the tart pan and the crumbs between your fingertips to make even and solid edges.
Baking the tart with a sheet of aluminum foil around the outside served a few functions. It prevents butter in the crust from leeching out and burning as the tart bakes.
The foil also helps keep the preserve-coated blueberries from falling off the top of the tart shell.
The finished tart is topped with a thick layer of shiny blueberries.
Ingredients
One 8.5-ounce package Biscoff cookies (about 2 1/2 cups of crumbs)*
1/2 cup (4 ounces) butter, melted
1/8 teaspoon salt
3 egg yolks
Grated zest of 2 key limes
One 14-ounce can sweetened condensed milk
1/2 cup key lime juice from about 1 pound of key limes
1 1/2 teaspoons powdered gelatin (about 1/2 packet of gelatin)
2 tablespoons cold water
2/3 cup blueberry or apricot jam
2 cups fresh blueberries, rinsed and drained
Fresh edible flowers and herbs as garnish
Directions
- For the Biscoff Crust: Grind the cookies in the bowl of a food processor fitted with the metal blade until finely ground. Pour the crumbs into a bowl. Add the melted butter and salt. Use a fork to stir the mixture until the crumbs are evenly moistened with the butter.
- Evenly distribute half of the crumb mixture into the bottom of a 14 x 4-inch rectangular or 8-inch round tart pan with a removable bottom. Press the crumbs into an even layer on the bottom of the pan. Add the remaining crumbs near the sides of the pan, pressing them evenly into the fluted rim.
- Cut a sheet of aluminum foil into a rectangle measuring approximately 22 inches long by 12 inches wide. Position the filled tart pan in the middle of the piece of foil. Lift the edges of the foil up around the outside of the pan, effectively creating a pan within a pan. Place it on a parchment-lined baking sheet.
- Bake at 350°F for 7-8 minutes until the crust is fragrant and slightly puffed. (The tart shell can be baked a day ahead and kept refrigerated before filling.)
- For the Key Lime Filling: In an electric mixer with the whip attachment, beat the egg yolks and lime zest on high speed until well aerated, about 5 minutes.
- Gradually add the condensed milk and continue to beat until thick, about 3 or 4 more minutes. Lower the mixer speed and slowly add the lime juice, stirring just until combined.
- Pour the mixture into the prepared crust. Bake at 350°F for 10-12 minutes until the lime mixture has just set. Cool completely on a wire rack, then chill thoroughly.
- To fill with the Blueberry Topping: Place the cold water into a small bowl. Sprinkle the gelatin on top. Let it sit for 5 minutes until the gelatin dissolves.
- Combine the jam and softened gelatin mixture in a small saucepan. Bring to a boil and cook until the gelatin melts, for 2-3 minutes.
- Pour into a mixing bowl and let cool for 5 minutes. Fold in the fresh blueberries.
- Spoon the fresh blueberry mixture on top of the baked filling. Use the edges of the foil to hold the berries in place. Chill for at least 30 minutes before serving garnished with edible flowers and herbs if you like.
Notes
* Biscoff are a type of Belgian speculoos spice cookie. If unavailable, use graham crackers instead. 17-18 whole rectangular graham crackers should yield 2 1/2 cups of crumbs after grinding.
