Cinnamon Roll Coffee Cake

Preheat the oven to 350°F (175°C). Grease or line a 9x13-inch pan with parchment paper for easy release.
With a mixer, cream softened butter and granulated sugar together until fluffy and slightly pale, about 2-3 minutes.
Add eggs one at a time, beating well after each. Beat in vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt.
Add dry ingredients to the butter mixture in three parts, alternating with the milk (begin and end with dry). Mix just until smooth; don’t over-mix.
Spread the batter evenly in the prepared pan (it will be thick).
For the cinnamon swirl, stir together melted butter, brown sugar, flour, and cinnamon in a bowl until smooth and thick.
Drop spoonfuls of the cinnamon mixture all over the cake batter. Use a butter knife or skewer to gently swirl the mixture throughout the cake—don’t over-mix; aim for a marbled effect.
Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs (not wet batter).
Let the cake cool for about 15 minutes. For the glaze, whisk powdered sugar with enough milk to make a thick but pourable icing. Drizzle over the still-warm cake. Let set slightly, then slice and serve.