1/2cupunsalted butter,melted (or 1 stick of butter, melted)
optional: sweetened condensed milk for topping
Preheat the oven to 375 degrees F. Line a 12-cup standard muffin tin with parchment paper liners (my personal favorite) or coat with nonstick spray. Then line a baking sheet with parchment paper or aluminum foil and set it aside.
For the streusel topping
In a medium bowl, add the granulated sugar, light brown sugar, ground cinnamon and salt. Mix together with a whisk.
Add the melted butter and whisk until well combined. Add the flour and mix everything together until moist.
Transfer the streusel topping to the prepared baking sheet and spread it out (this will help it dry out a little while you prepare the muffin mixture, which will make a more crumbly topping). The topping should have chunks of the mixture that are big and small. That's exactly what we want - an uneven crumbly streusel. Set aside until ready to use.
For the muffins
In a large bowl, add the flour, light brown sugar, baking powder, ground cinnamon, baking soda and salt. Whisk until well combined.
In a medium bowl, add the milk, Greek yogurt and eggs. Whisk until well combined. Add the wet ingredients into the dry ingredients and mix together until a thick batter is formed.
Pour the batter evenly into the muffin tins and top the muffins with the streusel topping. You may feel like you'll have leftover streusel, but press the mixture into the batter and try to use all of it.
Bake the muffins for 15 to 18 minutes, or until until a toothpick inserted into the center comes out clean. Remove the muffins from the oven and let them cool down for 5 minutes before serving.
Serve as is or top with a drizzle of sweetened condensed milk.