Preheat oven to 350 degrees F and line muffin tin with 18 paper cupcake liners.
In a medium mixing bowl, mix together flour, baking soda, baking powder, and salt. Set aside.
With an electric mixer, beat the butter and sugar together until fluffy. Add the milk, sour cream, eggs, vanilla, and zest and beat until thoroughly combined. Mix the dry ingredients in a little at a time until just combined.
In a small mixing bowl, combine 1 1/4 cup blueberries with 2 teaspoons flour until all are coated. Gently fold the blueberries into the batter.
Spoon the batter into the 18 cupcake liners (about 3/4 full).
Bake for 18-20 minutes or until a toothpick comes out clean.
For the Frosting:
Attach the paddle attachment to standing mixer (an electric hand mixer will work too). Beat butter and cream cheese together until smooth. Add the lemon juice, zest, salt, and beat in the powdered sugar a little at a time. Keep mixing until light and fluffy. Pipe frosting onto cooled cupcakes and then top with blueberries, lemon peel, and a mint leaf.
Store in an airtight container at room temperature up to two days or in the fridge for up to four days.
*To get eggs to room temperature quickly, just place the eggs (still in the shells) in a bowl of warm water for 5 minutes.