Preheat and prep: Heat your oven to 350°F (175°C). Line a large baking sheet with parchment. Draw two 8x8-inch squares as guides if you prefer layering without slicing.

Make the ladyfinger batter: In a bowl, whisk almond flour, coconut flour, baking powder, and salt. In another bowl, beat eggs and granular sweetener for 2–3 minutes until pale and slightly thick. Stir in melted butter, vanilla, and lemon zest. Fold in the dry mix until just combined.

Pipe or spread: For classic “finger” shapes, transfer batter to a piping bag and pipe 3-inch strips. Or simply spread the batter into two thin even rectangles using your parchment guides. Aim for about 1/4-inch thickness.

Bake: Bake 10–14 minutes until set and lightly golden at edges. Cool completely on the tray. If you made rectangles, trim to fit your dish (8x8-inch works well).

Make the lemon soak: Whisk lemon juice, water, powdered sweetener, and lemon zest until the sweetener dissolves. Taste and adjust sweetness.

Whip the cream: In a cold bowl, whip heavy cream to soft peaks. Don’t overbeat.

Make mascarpone filling: In a separate bowl, mix mascarpone, powdered sweetener, vanilla, lemon zest, lemon juice, and a pinch of salt. Stir until smooth. Gently fold in the whipped cream until creamy and spreadable.

Assemble layer one: Place the first sponge layer in your dish. Brush or spoon the lemon soak over the surface until lightly saturated but not soggy. Use about half the soak for the first layer.

Spread cream: Add half the mascarpone mixture and smooth it out to the edges.

Layer two: Add the second sponge layer. Brush with the remaining lemon soak. Spread the rest of the mascarpone over the top.

Chill: Cover and refrigerate for at least 4 hours, preferably overnight. This helps the layers set and the flavors blend.

Garnish and serve: Top with fresh lemon zest and thin lemon curls. Slice cleanly with a sharp knife. Serve chilled.