Preheat the oven to 350 degrees F.

In a small bowl, mash the sweet potatoes with a fork, and mix in the cream cheese, brown sugar if using, lemon juice, and pinch of salt until creamy. Remove the dough from the tube and separate into 4 rectangles. Working with 1 rectangle at a time, roll over the perforated lines in the dough to seal together. Cut the rectangle in half and then cut the halves into 2 triangles. Place a heaping teaspoon of sweet potato filling in the center of each of 4 triangles. Fold the dough over on each, as if you were making ravioli, and pinch the edges together. Cook's Note: Use a tiny bit of water if the dough is too dry to seal.

Continue making little triangle empanadas with the rest of the dough, 16 total. Place the triangles on a parchment-lined baking sheet and into the preheated oven. Bake the empanadas until golden, about 10 to 12 minutes. Meanwhile, in a shallow bowl, mix together the sugar, cinnamon, and pinch of salt. While still warm, brush the empanadas with melted butter, and then gently toss in the cinnamon-sugar mixture. Serve the empanadas with tangy plain yogurt for dipping.