Preheat your oven to 325°F (165°C) and line a loaf pan with parchment paper.

Cream together 1 cup of butter and 1 cup of white sugar until light and fluffy, 3-5 minutes.

Add 2 eggs and 2 teaspoons of vanilla extract, mixing until smooth.

Fold in 1 cup of sour cream and 1/2 cup of buttermilk until combined.

Sift together 2 cups of flour, 1 teaspoon of baking soda, 1 teaspoon of baking powder, and a pinch of salt, then mix into wet batter gently.

Prepare crumb topping by mixing 1/2 cup of flour, 1/4 cup of brown sugar, 1 teaspoon of cinnamon, a pinch of salt, and 4 tablespoons of softened butter until crumbly.

Pour half of batter into the loaf pan, sprinkle 2/3 of crumb topping, then add remaining batter and top with remaining crumb.

Bake for approximately 60 minutes, rotating halfway through, until a toothpick comes out clean.

Cool in pan for 1 hour, then transfer to wire rack. Mix 1 cup of powdered sugar with water for icing and drizzle over cake.