Coffee Cake Muffins

Prepare the crumb topping by mixing together flour, brown sugar, cinnamon, and a pinch of salt. Add melted butter and gently mix together until chunks form. Place into the refrigerator.
In a large bowl, combine sugar, brown sugar, oil, and melted butter. Whisk together for 1 minute, until combined. Then add eggs, sour cream, milk, and vanilla extract and continue to mix.
In a separate bowl, mix together the dry ingredients - combine flour, baking powder, baking soda, cinnamon, nutmeg, and kosher salt. Whisk together, then add to the wet ingredients and mix until just combined. Cover with plastic wrap and let the muffin batter sit for 30 minutes at room temperature.
While the batter is resting, preheat the oven to 375 degrees F. In a small bowl, combine cinnamon and sugar in a bowl and mix. Remove the streusel mixture from the refrigerator. Add muffin liners to every other muffin cup (so 6 total, see the picture above).
Spoon out 2 tbsp of the batter in a muffin cup. Sprinkle 1 to 1 1/2 tsp of the cinnamon sugar mixture on top of the batter, then scoop out an additional 2 tbsps of batter to place on top. Cover the top of the muffin with a generous amount of the crumb topping. Repeat with remaining muffins.
Bake one pan at a time for 23-26 minutes, until a toothpick comes out clean. Remove and allow the muffins to sit in the pan for 5 minutes, then remove and bake the remaining 6 muffins.