Preheat oven to 350°F (175°C). Grease or line a baking tin.
Whisk together flour, salt, and baking powder. Set aside.
Cream butter until smooth, then beat in sugar until light and fluffy.
Add eggs one at a time, mixing well and scraping the bowl between additions.
Mix in sour cream and vanilla until fully incorporated.
Add dry ingredients and mix just until combined. Use a spatula to fold in any unmixed bits. Avoid over mixing.
Pour batter into tin and smooth the top.
Bake for 40 minutes, or until a toothpick comes out clean from the center.
Cool in tin for 10 minutes, then transfer to a rack to cool completely.
