01 - Preheat the oven to 350°F (175°C). Grease and flour an 8-inch round cake pan.
02 - In a bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until evenly distributed.
03 - In a separate large bowl, beat the softened unsalted butter and granulated sugar together using an electric mixer until the mixture becomes light and fluffy.
04 - Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract until fully combined.
05 - Fold the finely chopped fresh basil into the wet mixture, distributing it evenly throughout the batter.
06 - Alternately add the dry ingredient mixture and the milk-yogurt blend to the wet mixture, beginning and ending with the dry ingredients. Mix gently until just combined, being careful not to overwork the batter.
07 - Pour the batter into the prepared cake pan and smooth the top with a spatula. Bake for 30–35 minutes, or until a toothpick inserted into the center emerges clean. Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
08 - While the cake bakes, combine the mixed berries, granulated sugar, and lemon juice in a small saucepan over medium heat. Cook for 8–10 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 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 cake. Spoon the berry compote on top just before serving, and garnish with extra fresh basil leaves or whole berries if desired.