01 - Preheat oven to 350°F. Grease and flour a 9-inch round cake pan.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, approximately 3 minutes.
04 - Add the eggs one at a time, beating well after each addition until fully incorporated.
05 - Stir in the finely chopped fresh basil and vanilla extract until evenly distributed throughout the batter.
06 - Add the dry ingredient mixture to the wet ingredients in three parts, alternating with the milk. Begin and end with the flour mixture. Mix until just combined — do not overmix.
07 - Gently fold the mixed berries into the batter using a spatula, taking care not to crush the fruit or overwork the batter.
08 - Pour the batter into the prepared cake pan and smooth the top. Bake at 350°F for 35 minutes or until a toothpick inserted into the center comes out clean.
09 - Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely. If desired, whip the heavy cream with powdered sugar and spread over the cooled cake. Garnish with fresh berries and basil leaves.