1. In the bowl of a stand mixer or using a hand mixer, combine the softened butter with the sugar until smooth. Add the milk, vanilla and egg and mix for another 2 minutes.
2. In a separate bowl, combine the flour, baking powder, and salt. Slowly add in the flour mixture and mix until just thoroughly combined. Shape the dough into 2 equal sized balls, wrap them with saran wrap and place into the fridge to chill for 30 minutes.
3. Preheat the oven to 400 F and line two baking sheets with parchment paper or a silicone baking mat. Working with the first ball of dough, roll the dough out on a very floured surface until about 1/4″ thick. Use a large cookie cutter to cut cookies out of the dough until the dough is all used and place them 2 inches apart on cookie sheets.
4. Place a teaspoon of jam in the center of each cookie. Roll out the second ball of dough and cut the same amount of cookies as prepared with the first ball. Top each cookie on the baking sheet with another cookie, and press the edges to seal. Use a fork to crimp the edges and ensure they’re sealed. Prick small holes with the fork into each of the cookies.
5. Bake the cookies for about 8 minutes, or until the edges are slightly browned. Remove the cookies from the oven and allow to cool on the cookie sheet for a couple of minutes, before transferring the cookies to a wire rack to cool completely.
6. Prepare the icing by combining the melted butter, vanilla, milk and powdered sugar until smooth. Add more milk or powdered sugar until you have a smooth consistency. Top each cookie with about a tablespoon of icing and allow to set.

Cookies will remain fresh in an airtight container for about a week, refrigerated for about two weeks and in the freezer for up to 2 months.