Preheat your oven to 375°F (190°C) and prepare a muffin tin by lining with paper liners or greasing it.

In a large bowl, whisk together the dry ingredients: flour, sugar, baking powder, salt, and cinnamon until well blended.

In another bowl, melt the butter and let it cool. Whisk it with milk, eggs, and vanilla until smooth.

Gently pour the wet ingredients into the dry ingredients and stir lightly until just combined.

In a small bowl, combine flour, brown sugar, and cinnamon for the streusel. Cut in the cold butter until crumbly.

Fill the muffin tins about 2/3 full with batter. Use a cookie scoop for uniform size.

Sprinkle the streusel topping over each muffin, pressing it gently into the batter.

Bake the muffins for 18-22 minutes until golden brown. A toothpick should come out clean.

Let the muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely.