In a medium mixing bowl, beat butter, cream cheese, and sugar with an electric mixer. Add flour, cinnamon, baking powder, and salt. Mix until just combined; don't overmix. Form dough into a smooth, flat disc, about 2 inches thick. Wrap in plastic and chill in the refrigerator for 1 to 2 hours, or make the dough a day or two  in advance and store in the refrigerator. Dough can also be made in advance and frozen; thaw in refrigerator overnight. To make the filling, mix together chopped walnuts, jam, and sugar. Preheat oven to 350ºF. Line a baking tray with parchment paper. Remove dough from the refrigerator. Sprinkle a little flour on a clean surface and place unwrapped dough on top. Sprinkle a little more flour on top and roll dough into a 12-inch square.  Cut dough into thirty-six 2-inch squares. Place about 1/2 teaspoon of filling in the center of each square and folder over to make a triangle. Use the tines of a fork to press and seal the edges. Place triangles on the prepared baking tray. Bake for 18 to 20 minutes or until the bottoms are lightly browned. Transfer cookies to a wire rack and let cool. When cookies are cool, sprinkle with powdered sugar.  Store in a covered container for up to a week.