Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners.

In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt.

In another bowl, mix the melted butter, milk, egg, and vanilla extract until smooth.

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

Evenly divide the batter among the muffin cups, filling each about two-thirds full.

In a small bowl, combine light brown sugar, flour, ground cinnamon, and cold butter, mixing until crumbly.

Sprinkle the streusel mixture over each muffin cup.

Bake for 18-20 minutes until a toothpick comes out clean and tops are golden.

Cool in the pan for 5 minutes, then transfer to a wire rack.