In a medium bowl, stir together the flour, brown sugar, sugar, cinnamon and salt until well combined. With your fingertips, work the butter into the flour mixture until it looks like wet sand with no large pieces of butter. Press the mixture together to form chunks. Set aside in the refrigerator until ready to use.

Preheat the oven to 350ºF (180ºC). Line a 9 x 5-inch loaf pan with parchment paper.

In medium bowl, stir together 1/2 cup (100g) of brown sugar and the cinnamon until well combined. Set aside.

In a separate medium bowl, whisk together the flour, baking powder, baking soda and salt until well combined.

In a large bowl, beat the butter, granulated sugar and the remaining 1/4 cup (50g) of brown sugar, with an electric mixer at medium speed, until light and fluffy. Beat in the eggs one at a time, making sure each one is fully incorporated. Beat in the vanilla extract.

In a small bowl or a glass measuring cup, whisk the milk and sour cream together. On low speed, beat the flour mixture into the batter in two additions, followed by half of the milk mixture after each addition. Mix just until combined.

Transfer half of the batter to the prepared loaf pan. Sprinkle half of the brown sugar-cinnamon mixture over the batter. Swirl with a skewer. Add the remaining batter and repeat with the remaining brown sugar-cinnamon mixture. Sprinkle the crumb topping on evenly.

Bake until a toothpick inserted into the center of the loaf comes out clean, about 50-60 minutes. (The toothpick may have some brown sugar or crumb topping on it, but not wet batter.) Let the loaf cool in the pan for 10 minutes, then transfer it to a cooling rack.

In a small bowl, whisk together the cream cheese, butter, powdered sugar, vanilla extract, salt and 1 tablespoon (30ml) of milk until smooth. Whisk in additional milk if needed to achieve your desired consistency. Drizzle the icing over the cooled loaf.