Preheat the Oven: Preheat your oven to 350°F (175°C). Line a muffin tin with muffin liners or lightly grease with cooking spray.
Prepare the Muffin Batter: In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt. In another bowl, whisk together the melted butter, milk, egg, and vanilla extract. Add the wet ingredients to the dry ingredients and mix until just combined. Be careful not to overmix.
Prepare the Cinnamon Filling: In a small bowl, mix together the softened butter, brown sugar, and ground cinnamon until smooth.
Assemble the Muffins: Fill each muffin cup about halfway with the muffin batter. Add a spoonful of the cinnamon filling on top of the batter in each cup. Top with the remaining muffin batter, filling each cup almost to the top. Using a toothpick or skewer, swirl the batter and filling together to create a marbled effect.
Bake the Muffins: Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Remove from the oven and let the muffins cool in the tin for a few minutes before transferring them to a cooling rack to cool completely.
Prepare the Cream Cheese Glaze: In a medium bowl, beat the softened cream cheese with a hand mixer until smooth. Add the powdered sugar, milk, and vanilla extract, and mix until well combined and smooth. Add more milk if needed to reach a drizzling consistency.
Glaze the Muffins: Once the muffins are cooled, drizzle the cream cheese glaze over the top of each muffin using a spoon or a pastry bag.
Serve and Enjoy: Serve the cinnamon roll muffins warm or at room temperature. Enjoy the delightful blend of soft muffin, sweet cinnamon filling, and creamy glaze!