Blueberry swirl cupcakes

Sugar, granulated	6 tablespoons + 2/3 cup
Sugar, dark brown	¼ cup
Cinnamon	1 teaspoon
Flour, cake	1 2/3 cups
Baking soda	¼ teaspoon
Baking powder	1 teaspoon
Salt, fine sea	½ teaspoon
Butter, unsalted, softened	8 tablespoons + 10 tablespoons
Eggs	2 large
Vanilla extract	1 teaspoon + ½ teaspoon
Sour cream, room temperature	¾ cup
Blueberries	6 ounces
Cream cheese, room temperature	8 ounces
Sugar, confectioners’, sifted	2 2/3 cups
Blueberry jam, strained	¼ cup

1. Preheat to 375°F; set a rack in the upper third of the oven. 
2. Line a standard 12-cup muffin tin with baking cups. 
3. In a small bowl, combine the 6 tablespoons granulated and dark brown sugars with the cinnamon; set aside. 
4. Sift together the flour, baking soda, baking powder, and salt. 
5. Cream the 8 tablespoons butter and 2/3 cup sugar together with a mixer on medium-high speed, until pale and fluffy, about 2 to 3 minutes. 
6. Beat in the eggs, one at a time, and then add the vanilla, scraping down the sides of the bowl. 
7. Reduce to low speed, and beat in a third of the flour mixture, half the sour cream, another third of flour, remaining sour cream, and then the remaining flour. 
8. Fold the blueberries in by hand. 
9. Divide the batter among the baking cups. 
10. Add the topping, pressing gently to ensure it sticks to the batter. 
11. Bake for 20 minutes, or until golden and a toothpick comes out with moist crumbs. 
12. Remove the cupcakes from the tin, and let cool on a wire rack. 
13. Cream the 10 tablespoons butter and cream cheese together in a mixer on medium-high, until pale and fluffy, about 2 minutes. 
14. Reduce to low, add the vanilla, and gradually add the confectioners’ sugar. 
15. Increase speed to medium-high, and beat 1 minute. 
16. Spoon the jam on top of the icing, and without stirring, spoon the icing into a pastry bag. 
17. Pipe swirled mounds of icing on top of each cupcake.

Consume within 6 hours for maximum happiness.