Preheat the oven to 350. Line a loaf pan with parchment and spray with cooking spray.
In a large bowl or the bowl of a stand mixer, beat together the butter and sugar until light and fluffy. Add the eggs and vanilla and beat until smooth. Add the baking powder, salt, and flour, and mix until just combined. Add the sour cream, and mix until smooth. Spread the batter evenly in the prepared pan.
Bake 50-60 minutes, until golden brown on top and a toothpick inserted in the center comes out clean. Let cool 10-15 minutes, then remove to a cooling rack to cool completely.
To serve, cut into slices and serve with whipped cream and berries, if desired.