Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a mixing bowl, cream together the butter and sugar until light and fluffy. Add the egg and vanilla extract, and mix until combined.
In another bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, alternating with the milk, until just combined.
Drop spoonfuls of dough onto the prepared baking sheet, spacing them about 2 inches apart. Flatten each mound slightly with the back of a spoon.
Bake for 10-12 minutes, or until the edges are lightly golden. Remove from the oven and let cool completely on a wire rack.
Once the cookies are cool, spread a generous amount of marshmallow creme on the flat side of half of the cookies. Top with the remaining cookies to form sandwiches.
Dip each sandwich into the melted chocolate, covering completely. Place on a wire rack to set.
Enjoy your homemade Southern Moon Pies!