Butter Cookies with Mocha Frosting

Directions

1. 1
   Using an electric or stand mixer, cream together the butter and sugar.
2. 2
   Add in the vanilla and egg, and beat until fully mixed in.
3. 3
   Whisk together the flour, baking powder, and salt.
4. 4
   Add half of it to the bowl with the butter mixture. Beat briefly on low to incorporate.
5. 5
   Add the milk and beat for 10 seconds.
6. 6
   Add the rest of the flour mixture and mix until just incorporated, adding more milk by tablespoon if necessary.
7. 7
   Divide the dough into 3 equal parts and roll them into logs with a diameter of 1 1/2 inches. Wrap in plastic wrap and refrigerate for at least 2 hours and up to a day. The dough logs can also be frozen for about a week.
8. 8
   Preheat the oven to 375 degrees F and line baking sheets with parchment paper. Slice the logs into cookies and bake for about 10 minutes, until the edges are slightly golden. Cool on a wire rack.
9. 9
   Melt the chocolate in a microwave in 30 second bursts, stirring in between. Set aside.
10. 10
    Cream the butter until fluffy.
11. 11
    Add the powdered sugar, one cup at a time, alternating with the cream, one tablespoon at a time.
12. 12
    Add the melted chocolate, espresso, vanilla, and salt, and beat until fully incorporated.
13. 13
    When the cookies are completely cooled, frost each one with frosting, and add the optional sprinkles. Store in an airtight container.