Using a stand mixer with a paddle attachment or hand mixer, cream together butter and granulated sugar for a few minutes. The mixture should be light and airy.
Step 2.
Add an egg and vanilla extract. Mix it again for a couple of minutes until well combined.
Step 3.
Add all-purpose flour and salt and mix on low speed until just combined. Make sure you don't overmix the dough!
Step 4.
Add 2 teaspoons milk and mix. The dough should be a pipeable consistency but not runny. You can add more milk if needed, but try to use as little milk as possible.
Step 5.
Transfer the dough to a piping bag with a large piping tip. Pipe 2-inch swirls on a baking sheet, 3 inches apart. Bake.
Step 6.
When done, remove from the oven and let them sit on the baking sheet for about 10 minutes, then transfer to a wire rack to cool off completely.
Step 7.
Dip 2/3 of the cookies into melted chocolate and place on a parchment paper. Decorate with sprinkles and let them dry off completely.