In a medium bowl, combine 3/4 cup all-purpose flour, brown sugar, and ground cinnamon. Cut in the cold, cubed butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Set aside.

Preheat your oven to 375°F (190°C). Grease and flour a 9x13 inch baking pan, ensuring it's evenly coated.

In a large bowl, whisk together 2 cups all-purpose flour, granulated sugar, baking powder, and salt. Set aside.

In a separate large bowl, using an electric mixer on medium speed, cream together the softened butter until light and fluffy (about 2-3 minutes). Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix on low speed until just combined and no streaks of flour remain; be careful not to overmix.

Spread half of the coffee cake batter evenly into the prepared baking pan.

Sprinkle half of the prepared streusel mixture evenly over the batter.

Carefully dollop and spread the remaining coffee cake batter over the streusel layer. It helps to drop spoonfuls of batter over the streusel and gently spread them to cover. Sprinkle the remaining streusel mixture evenly over the top layer of batter.

Bake for 40-45 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean. If the topping begins to brown too quickly, you can loosely tent the pan with aluminum foil.

Let the cake cool in the pan on a wire rack for at least 30 minutes before glazing.

In a small bowl, whisk together the powdered sugar, milk (starting with 2 tablespoons), and vanilla extract until smooth. Add more milk, a teaspoon at a time, until the glaze reaches your desired drizzling consistency.

Drizzle the glaze evenly over the still-warm or completely cooled coffee cake. Slice and serve warm or at room temperature.