Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners then spray with nonstick spray. Set aside.
To make the crumb topping, combine the sugars, cinnamon and salt in a medium bowl. Whisk in melted butter then stir in the flour using a rubber spatula. Spread the mixture out on a parchment-lined baking sheet to dry until crumbly and ready to use.
To make the muffins, in a large bowl, combine flour, sugar, baking powder, baking soda, cinnamon, and salt and set aside.
In a medium bowl, whisk together the milk, melted butter, vanilla and eggs. Pour mixture over the dry ingredients and stir using a rubber spatula until just incorporated, being careful not to over-mix.
Scoop the batter evenly into the muffin cups until they're about 2/3 of the way full. Generously top each with the reserved crumb topping, using your fingers to gently press the crumbs into the batter to help it stay in place while baking. It will be a lot of crumb topping on each muffin. That's what you want!
Bake muffins in preheated oven for 10 minutes, then reduce the heat to 350°F degrees and bake another 10-12 minutes until set and a toothpick inserted in the center comes out clean.
While the muffins are baking, make the glaze. Combine powdered sugar and milk in a medium bowl and whisk until smooth. If the glaze is too thin, add more confectioners' sugar as needed.
When the muffins are done, cool for 10 minutes and drizzle the glaze on each muffin using a small spoon.