Preheat the oven to 350 F (177 C). Grease and line the bottom of a 8 inch (20 cm) or 9 inch (23 cm) springform or cake pan with parchment paper.

In a small bowl, melt the butter and set aside to cool to room temperature (about 15 minutes).

In a mixing bowl, whisk together the flour, baking powder and salt until well combined.

In a large mixing bowl whisk the eggs and sugar until smooth. Continue whisking until the eggs and sugar mixture thickens and lightens to a ribbon stage.

Whisk in the vanilla extract and sour cream until smooth and well combined.

Alternating dry ingredients and melted butter, mix in ⅓ of the dry ingredients into the wet, followed by ½ of the melted butter. Repeat until all the ingredients are just combined.

Fold in most of the mixed berries. Reserve ½ cup of the fresh or frozen berries for topping.

Evenly spread the berry cake batter into the prepared pan. Top with the reserved berries and more sugar if desired.

Bake the berry filled cake for 45 - 55 minutes or until a toothpick inserted into the center comes out clean.

Cool the cake in the pan for 10 - 15 minutes. Gently remove the cake from the pan and allow it to cool for 10 - 15 additional minutes.

Transfer the sweet berry cake to a serving plate, top with powdered sugar, slice and enjoy.