Preheat your oven to 350°F (175°C) and grease a muffin tin or line it with paper liners.

In a large bowl, whisk together the flour, granulated sugar, baking powder, salt, and ground cinnamon until combined.

In another bowl, mix the milk, vegetable oil, and eggs until smooth.

Gently fold the wet ingredients into the dry ingredients until just combined. Be careful not to overmix; a lumpy batter is what you’re aiming for.

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

Spoon a tablespoon of muffin batter into each muffin cup, then add a small dollop of the cinnamon filling on top, followed by another tablespoon of batter on top of that, gently keeping it layered.

Using a skewer or a toothpick, swirl the filling slightly to create a beautiful marbled effect in each muffin cup.

Place the muffin tin in the oven and bake for approximately 18-20 minutes or until a toothpick comes out clean from the center.

While the muffins cool, whisk together the powdered sugar, milk, and vanilla extract to make the icing.

Once cool, drizzle the icing over the muffins, and enjoy your heavenly Muffin Cinnamon Rolls!