Preheat your oven to 375°F (190°C). Prepare your muffin tin by spraying with non-stick spray or using paper liners.

Combine all-purpose flour, granulated sugar, baking powder, and salt in a large mixing bowl and whisk until well blended.

In a separate bowl, mix together milk, melted butter, egg, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and fold gently together until just combined.

In a small bowl, mix brown sugar, ground cinnamon, and melted butter to create the cinnamon filling.

Fill each muffin cup halfway with batter, then add a dollop of cinnamon filling, and top with more batter until two-thirds full.

Swirl the cinnamon mixture into the batter with a toothpick or knife.

Bake for 15 to 18 minutes until golden brown and a toothpick comes out clean.

Let muffins cool for a few minutes, then drizzle with cream cheese glaze if desired before serving.