Preheat your oven to 350°F (175°C). Prepare a round baking pan by greasing it lightly with butter and a dusting of flour.

In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy (about 3-5 minutes).

Add the eggs one at a time, mixing well after each addition.

In another bowl, mix together the flour, baking powder, and a pinch of salt. Gradually add these dry ingredients to the wet mixture, alternating with the milk.

Stir in the vanilla extract until well blended.

Gently fold in the mixed berries, being careful not to break them apart too much.

Pour the batter into the prepared pan and spread it evenly.

Bake for about 25-30 minutes or until a toothpick comes out clean.

Cool in the pan for about 10 minutes, then turn it out onto a wire rack to cool completely.

Whip the heavy cream and powdered sugar together until soft peaks form.

Once the cake is completely cool, spread the whipped cream over the top. Garnish with mixed berries and fresh mint leaves if desired.