Preheat the oven to 350°F (175°C). Grease and flour a cake pan.

In a mixing bowl, cream together the softened butter and sugar until light and fluffy.

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

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, alternating with the milk, and mix until just combined.

Gently fold in the mixed berries, banana, and apple into the batter.

Pour the batter into the prepared cake pan and smooth the top.

Bake in the preheated oven for 30 minutes or until a toothpick inserted into the center comes out clean.

Let the cake cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Serve slices of the cake topped with whipped cream.