Preheat the oven to 350 F. Set the berries in a baking pan that’s either 8x8 or 9x9.

Roast the berries until some have burst, the liquid at the bottom of the pan has thickened - about 20-25 minutes. Let cool for 10 minutes.

Set the berries in a food processor and puree.

Add the sour cream and puree the mix until smooth. Set aside to cool completely.

Prepare a 5x9 inch loaf pan by greasing it and lining it with parchment paper.

In a large bowl melt the butter. Add the sugar, salt, lemon zest and vanilla and whisk very well.

Whisk in the eggs, vigorously, the mix should turn thick and shiny. If it breaks, this means the eggs were too cold (they should be at room temperature).

Whisk the blueberry sour cream mix until the batter is even, then stir in the flour (sift it in if it’s lumpy) and baking powder.

Pour into the prepared pan and sprinkle the granulated sugar on top. The oven should be at 350 F for baking. Bake the loaf cake until a cake tester comes out clean, about an hour. Let cool slightly in pan then transfer to cooling rack.