Preheat the oven to 375 degree F. Brush a muffin tin with melted butter or spray with nonstick spray and sprinkle with flour.
In a large bowl, whisk together the flour, baking powder, nutmeg, salt and baking soda. In a small bowl or measuring cup, whisk together the milk, yogurt and vanilla extract.
In the bowl of your electric mixer (fitted with the paddle attachment), beat the butter and sugar until light and fluffy, about 2 to 3 minutes. Beat in each egg until combined, scraping down the sides and bottom if needed. With the mixer on low speed, add 1/3 of the dry ingredients, then 1/2 of the milk. Add another 1/3 of the dry ingredients and the rest of the milk. Finish with the remaining dry ingredients. Scoop the mixture into the muffin tins, filling them 3/4 of the way full. Bake for 15 to 20 minutes, or until they are set on top and golden. Let the muffins cool for 5 minutes, then remove from the tins and cool almost completely.
Brush the muffins with the melted butter (all over the sides too!) and sprinkle with the cinnamon sugar.