Preheat oven to 350°F (175°C). Grease two 9-inch round cake pans and line bottoms with parchment if you like easy removal.

In a large bowl, whisk or use a mixer to beat the 3 eggs with 1 cup sugar until pale and ribbon-like — about 3–5 minutes.

Stir in the melted 1/2 cup butter and 1 teaspoon vanilla extract until combined.

In a separate bowl, whisk together 1 1/2 cups flour, 1 teaspoon baking powder, and a pinch of salt.

Gradually fold the dry ingredients into the egg mixture until just blended. Avoid overmixing to keep the cake tender.

Divide batter evenly between the prepared pans. Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.

Remove from oven and let the cakes cool in pans for 10 minutes, then turn out onto a rack to cool completely.

While cakes cool, blend 2 cups blackberries until smooth and strain through a fine mesh sieve to remove seeds. Reserve 1 cup of puree for the glaze.

Chill your mixing bowl for 10 minutes if possible. Whip 2 cups heavy cream to stiff peaks.

Fold the blackberry puree, 1/2 cup vanilla yogurt, and 1 teaspoon vanilla extract into the whipped cream until uniform and airy.

Place one sponge layer on a serving plate. Spread or pipe half the mousse evenly on top, then cover with the second layer.

In a small saucepan, combine 1 cup blackberry puree, 1/4 cup sugar, and 1 tablespoon lemon juice. Bring to a simmer and cook until slightly thickened, about 4–6 minutes.

Pour the cooled glaze over the assembled cake, allowing it to drip down the sides. Refrigerate for at least 2–3 hours to set before slicing.