1. Preheat oven to 350ºF / 180ºC.
2. Butter or spray a 9x4-inch loaf pan or a 9-inch square pan.
3. Line with parchment paper if wanted.

For the streusel

1. In a small bowl mix all ingredients together until the mixture resembles wet sand. Reserve.

For the cake

1. Melt butter in a saucepan with high sides, at medium heat, until it begins to foam.
2. Bubbles will appear and a chirping noise will begin. Let it boil away until the bubbles and noise subside and the surface covers with foam.
3. Lower the heat and watch carefully, twirling the pan a few times until a nutty smell appears and, beneath the foam, the butter is amber colored. Be careful not to burn it!.
4. You have brown butter now. Transfer it to a medium bowl and let cool slightly.
5. Add the milk (first to lower the temperature), the eggs, and sour cream to the warm butter and mix lightly.
6. In a large bowl sift together flour, baking powder, baking soda, and salt. Add both sugars and mix to combine.
7. Make a well in the center and add the wet ingredients.
8. Mix with a spatula until combined, like you would a muffin mix, but careful not to overmix.
9. Spoon half of this batter in the prepared pan.
10. Sprinkle with half the streusel mixture.
11. Cover with the other half of the batter and end with the remaining streusel.
12. Bake for 40-45 minutes, depending on the pan you use until a tester comes out clean.
13. The loaf pan might take a bit more.
14. Let cool for 10 on a wire rack and carefully unmold. Some sugar might be stuck to the sides.

For the glaze

1. Mix sugar and liquid until creamy and lump free.
2. Drizzle over the cake.
3. Keep wrapped at room temperature for a few days.