Preheat your oven to 350℉.

In your mixer or with your hand-held mixer, cream together the butter and sugar until light and fluffy on medium speed - 2 or 3 minutes.

To the same bowl on medium-low speed, beat in the eggs one at a time, then the milk, and finally the vanilla extract, until all combined.

In a separate bowl, combine the flour, baking powder, salt, and cinnamon - give it a little mix with a fork or spoon. Then on low speed (so it doesn't poof out everywhere), gradually add the dry into the wet mixture until just combined.

Grease and line 9 spaces in your muffin tin and pour the batter evenly in them (about ½ cup in each).

To make the streusel topping:In a small bowl (can be the same as you used to mix the dry ingredients) add the melted butter, flour, light brown sugar, cinnamon, and salt until combined - it'll be a sandy-like texture that sticks together when you clump some together. Sprinkle evenly across all the 9 muffins, clumping some together as you go.

Bake the muffins in a preheated 350℉ oven for about 18-22 minutes until golden and a tester comes out clean.