• Preheat the oven to 350°F and line a muffin tin with liners. Very, very lightly spray with non-stick cooking spray if desired.

Cinnamon Sugar Filling - Optional, if you want cinnamon layer inside muffins

• In a small bowl, mix together sugar, melted butter and cinnamon; set aside.

Crumble on top

• Mix together the sugars, cinnamon and salt in a medium bowl. Whisk in melted butter. Add flour and stir using a rubber spatula just until moist. Spread out mixture on parchment paper to dry until ready to use.

Coffee Cake Muffin Batter

• In a large mixing bowl, whisk together eggs and sugar. Add in melted butter, Greek yogurt and vanilla extract mixing until smooth.
• Add in flour, baking powder, baking soda, and salt. Mix until well combined.

Assembly

• Begin to assemble the batter inside the lined muffin tin by scooping about 2 tablespoons of muffin batter into each muffin cavity. I like to use a small scoop, works easily if you have one!
• Place a tablespoon of cinnamon sugar mixture on top of each, then top each with 1 to 2 tablespoons of muffin batter, filling the tin 3/4 of the way to the top. (You get 12 if large muffins if you use all the batter. If you use less, you could get 16 - 18 muffins and bake them accordingly, by decreasing the timer 5-10 minutes.)
• Sprinkle muffins with crumb topping, using your fingertips to gently press the crumbs into the batter. Place into oven and bake for 15-17 minutes, or until a tester inserted in the center comes out clean.
• Allow muffins to cool down to room temperature in the pan prior to transferring them to a wire rack to glaze.
• Drizzle a little glaze over warm or cooled muffins.

Vanilla glaze

• Mix together the powdered sugar and cream/milk together to get a smooth glaze. Drizzle on top if desired.
• Warm these up in the microwave and enjoy with your cup of coffee or juice!