Note: I use a food processor to make my pie and galette crusts. If you choose to do the same, the biggest thing to remember is to not over-process, as this toughens the crust when baked.
Combine the flour, salt, and baking powder in the bowl of a food processor fitted with a metal blade. Give it a whirl to disperse the baking powder and salt through the flour.
Add the butter and cream cheese all at once. Pulse a bunch of times until the butter is pea-sized.
Add the ice water and vinegar all at once and pulse until it starts to pull together as a dough. This should only take 8 - 10 pulses. It won't be a solid dough yet.
Spill it out onto a lightly floured countertop and smear the dough 3 times using the heel of your hand. Divide into four equal pieces, and shape into four disks. Wrap in wax paper and chill for at least 30 minutes.
Preheat the oven to 400˚F, and line a baking sheet with parchment paper. Roll out each disk of dough between two pieces of wax paper. If the disks become sticky from the butter or cream cheese, sprinkle a little flour on top of the dough and replace the wax paper. Place two disks on the parchment paper lined baking sheet, and spread 1 cup of Filling (recipe below) on each of them. Cover them with the other disks, pinch the edges together to form a seal, and gently fold the edges up. Cut a few slits on the edges of the galettes to allow steam to be released during cooking.
Carve a pattern with a sharp knife on the tops of the galettes if you want, and then baste them with butter and sprinkle a little turbinado raw sugar on top.
Bake for 20 - 25 minutes, or until the crusts are well-browned. Allow to cool slightly before slicing.
