01 - Preheat the oven to 350°F (175°C). Grease and flour an 8-inch round cake pan, ensuring even coverage to prevent sticking.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until evenly distributed.
03 - In a large mixing bowl, beat the softened unsalted butter and granulated sugar together using an electric mixer on medium speed until pale, light, and fluffy — approximately 3 to 4 minutes.
04 - Add the eggs one at a time, beating thoroughly after each addition until fully emulsified. Stir in the vanilla extract.
05 - Gently stir the finely chopped fresh basil into the wet mixture, distributing it evenly throughout the batter.
06 - Alternately add the dry ingredient mixture and the whole milk mixed with Greek yogurt to the wet batter, beginning and ending with the dry ingredients. Fold gently until just combined — do not overmix.
07 - Pour the batter into the prepared cake pan and smooth the surface with a spatula. Bake for 30 to 35 minutes, or until a toothpick inserted into the center emerges clean. Allow the cake to rest in the pan for 10 minutes, then turn it out onto a wire rack to cool completely.
08 - While the cake cools, combine the mixed fresh berries, granulated sugar, and lemon juice in a small saucepan over medium heat. Cook for 8 to 10 minutes, stirring occasionally, until the berries soften and the mixture thickens slightly. Remove from heat and let cool completely.
09 - In a chilled bowl, beat the cold heavy cream with an electric mixer until soft peaks begin to form. Add the powdered sugar and finely chopped fresh basil, then continue beating until stiff peaks hold their shape.
10 - Spread the basil whipped cream evenly over the fully cooled sponge. Spoon the cooled berry compote over the cream just before serving. Garnish with additional fresh basil leaves or whole berries if desired.