Step 1In the bowl of a food processor, combine the butter, cream cheese and flour and pulse until it forms a soft ball. Halve the ball and sprinkle the halves with flour. Wrap the balls and refrigerate the dough overnight to chill.
Step 2Heat the oven to 350 degrees. Fill a baking pan or shallow mixing bowl with powdered sugar to coat the finished cookies.
Step 3On a heavily floured surface, roll the dough to a thickness of one-eighth inch. Cut the dough into 3-inch thick rounds using a cookie cutter or glass. Spoon about 1 teaspoon jam in the center of each circle. Fold the circle into a moon shape and press the edges closed with your fingers (if the dough won't seal, wet the edge with a little water to make it sticky). Use a fork to seal the edges completely.
Step 4Place the cookies about 2 inches apart on a parchment-lined cookie sheet. Bake until set but not browned, 8 to 10 minutes.
Step 5Remove the cookies from the oven and cool on the baking sheet for 1 minute, then place in the powdered sugar to coat.