For the cupcakes:
Preheat the oven to 350°F. Line a standard 12-cup muffin tin with paper liners.
In a large bowl, sift the flour and baking powder. Add in the salt.
In the bowl of an electric mixer, beat the sugar and butter on medium-high speed until light and fluffy, about 3 minutes. Add the eggs and vanilla and beat until well combined. Add the sour cream and then the flour mixture, beating well after each addition. Continue beating for another minute, or until the batter is thoroughly mixed.
Fill each muffin cup 2/3 full. Bake for 18 minutes, or until a toothpick inserted into the center comes out clean. Let cool for 10 minutes in the pan on a rack before removing the cupcakes to the rack to cool completely.
For the frosting:
In the bowl of an electric mixer, beat the butter on medium-high speed until light and fluffy, about 2 minutes. Add the sugar and vanilla and beat until very smooth and creamy, about 3 minutes. Add in the flour and salt and beat until combined. Add in the milk, 1 tablespoon at a time, until you reach the desired consistency.
Spread or pipe the frosting onto the cupcakes. Sprinkle with the chocolate chips. Serve or store the frosted cupcakes in an airtight container in the fridge for up to 3 days. Bring to room temperature before serving.