Spring-Fresh Elderflower Yogurt Cake with Rhubarb-Strawberry Compote

Preheat oven to 180°C (350°F). Grease a 26cm (10-inch) springform pan and line with parchment paper. Beat eggs and sugar for 8-10 minutes until pale and voluminous. Sift flour, cornstarch, and baking powder together, then gently fold into the egg mixture.

Pour batter into prepared pan and smooth the surface. Bake for 20-25 minutes until golden brown and springs back when lightly pressed. Cool completely on a wire rack, then remove from pan.

Cook rhubarb with sugar and lemon juice in a saucepan over medium heat for 5 minutes. Add strawberries and cook for another 3-4 minutes until fruit is tender but still has some bite. Let cool completely.

Soak gelatin sheets in cold water for 5 minutes. Warm 3 tbsp yogurt in a small saucepan (don't boil!). Squeeze out gelatin and dissolve in warm yogurt. Strain through a fine sieve into a small bowl and let cool slightly.

Mix remaining yogurt with powdered sugar and 4 tbsp elderflower syrup. Stir in the gelatin mixture. Whip cream to soft peaks and gently fold into yogurt mixture. Chill mousse for 10 minutes to thicken slightly.

Place sponge base in clean springform pan. Mix elderflower syrup with water and brush over sponge. Spread half the yogurt mousse over base, then distribute compote evenly. Top with remaining mousse, smoothing the surface.

Refrigerate cake for at least 4 hours or overnight until set. Carefully remove from pan before serving. Decorate with fresh elderflowers or strawberries if desired.