
Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners.
In a large bowl, whisk together flour, granulated sugar, baking powder, salt, and cinnamon.
In another bowl, combine melted butter, milk, eggs, and vanilla; mix well.
Pour the wet ingredients into the dry mixture and stir until just combined.
For the streusel, mix flour, brown sugar, and cinnamon; cut in cold butter until crumbly.
Fill muffin cups with batter and top generously with streusel.
Bake for 20–25 minutes until golden brown and a toothpick comes out clean.
Cool slightly before enjoying.