For the cinnamon cake:

1. Preheat the oven to 350°F/180°C
2. Place paper liners in the muffin tins or grease the pans. 
3. Cream the butter in a large bowl while gradually adding the sugar. Beat for 3 minutes, until fluffy and light. You can use an electric or stand mixer. 
4. Add the egg yolks, one at a time, mixing well after each one. 
5. Sift the dry ingredients (flour, baking powder and soda, and salt) and the cinnamon. 
6. Add in 3 parts to the butter mixture, alternating with the sour cream in 2 parts. This means you start and end with flour. 
7. Don’t overheat at this point. The dry ingredients should be mixed *just* until well integrated. 
8. In a separate clean and dry bowl, beat egg whites until stiff peaks form. 
9. Add 1/3 of the whites to the cake batter and mix with a rubber or silicon spatula. 
10. Before it’s completely incorporated, add another 1/3 and mix. Repeat with the last part. Mix until no streaks of white remain but don’t overdo it. 
11. Divide evenly between the paper liners, filling no more than 3/4 of their capacity. 
12. Bake for 20-25 minutes, or until a cake tester or toothpick comes out clean. 
13. Let cool completely on a wire rack before frosting. 

For the cinnamon frosting:

1. Beat cream cheese and butter in a medium bowl until smooth and creamy. 
2. Add half of the powdered sugar amount and the cinnamon. Mix well. 
3. Add more sugar until it’s a thick consistency. Don’t add too much before trying it out and making sure you can pipe it easily. 
4. Add vanilla if using it. 
5. If the frosting is too loose, add more sugar, a tablespoon at a time. 
6. Frost cupcakes right before serving them and sprinkle with cinnamon sugar (mix 1 tablespoon regular or brown sugar and 1/2 teaspoon cinnamon in a small bowl) or just cinnamon if you want to.