Prepare the strawberry sauce by chopping strawberries, mixing with lemon juice and erythritol, heating over medium until syrupy, and let cool.

Preheat oven to 350°F. Beat butter and erythritol until creamy. Add yolks and vanilla, then mix in coconut flour, baking powder, and salt.

Whip egg whites until stiff peaks form and gently fold into the batter. Spoon into prepared tin and smooth the top.

Bake for 25 minutes or until golden and springs back. Cool for 10 minutes before transferring to a wire rack.

Beat mascarpone and whipping cream until thick. Mix in erythritol and vanilla until fluffy.

Assemble by layering strawberry sauce, sponge pieces, cream, and sliced strawberries, finishing with cream on top.

Chill assembled tiramisu for at least 1 hour before serving. Enjoy chilled.