In a small bowl, whisk together 1/2 cup all-purpose flour, 1/2 cup brown sugar, and 1 tablespoon ground cinnamon. Add 1/4 cup cold, cubed butter. Use your fingertips to cut the butter into the mixture until it resembles coarse crumbs. Set aside.

Preheat your oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan. In a large bowl, whisk together 1 1/2 cups all-purpose flour, 3/4 cup granulated sugar, 2 teaspoons baking powder, and 1/2 teaspoon salt.

In a separate medium bowl, whisk together 1/2 cup milk, 1 large egg, 1/3 cup melted butter, and 1 teaspoon vanilla extract.

Pour the wet ingredients into the dry ingredients. Stir only until just combined – do not overmix.

Spread half of the batter into the bottom of the prepared loaf pan. Sprinkle with half of the streusel topping. Add the remaining batter on top and finish with the rest of the streusel.

Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean. Let it cool in the pan for 15 minutes before moving it to a wire rack to cool completely.