In the bowl of a stand mixer, cream together the butter, shortening, and sugar until smooth. Mix in the egg, egg yolk, and molasses. Add in the flour, baking powder, and salt until incorporated. Stir in the chopped white chocolate. Chill the dough for 30-60 minutes.
Preheat the oven to 375 degrees. Using a tablespoon-sized cookie scoop, portion the dough onto a parchment-lined baking sheet. Gently flatten each ball of dough. Bake for 11 minutes or until set. Remove from oven and let cool for 2-3 minutes on the baking sheet before transferring to a rack to cool completely.
Melt the candy melts according to package directions. Dip each cookie in the white chocolate, covering half of the cookie. Place covered cookie on a parchment-lined baking sheet to set. Store in an airtight container.