Place racks in the upper and lower thirds of the oven and preheat to 425°Line 4 baking sheets with parchment paper (or cook in batches).
Mix the sugar, cinnamon, and salt together in a bowl.
Sprinkle a light coating of flour on your countertop, then spread 1 cup of the cinnamon-sugar mixture on top, right where the puff pastry will go. Place the puff pastry in the center of the cinnamon-sugar mixture. Lightly flour your rolling pin and roll the puff pastry out into a large rectangle, about 12-by-26-inches with a 1/4-inch thickness, adding a bit of flour as needed while you roll. Sprinkle the top with the remaining cinnamon-sugar mixture.
Mark a line horizontally across the center of the puff pastry with a knife or ruler, without cutting all the way through. Roll the bottom of the puff pastry toward the center line, creating a layered spiral. Repeat with the top of the puff pastry, rolling in toward the center line, then press both rolls towards the center. The shape should resemble a pretzel.
Cut in half horizontally, across the two rolls, and wrap in plastic wrap. Place in the refrigerator for at least 30 minutes. Scrape any leftover cinnamon-sugar mixture onto a small plate.
Slice the chilled rolls into 1/2-inch slices. Dip both sides of slices in the remaining cinnamon-sugar mixture and place on a baking sheet, making sure to leave about an inch between the slices.
Bake for 10 to 12 minutes, then remove from the oven, flip the orejas, and return to the oven (swapping the baking sheet that was on top with the bottom). Bake for 10 to 12 minutes more, until both sides are golden brown. Transfer to a metal cooling rack and cool completely.
While the orejas are cooling, bring the heavy cream to a simmer in a small pot. Place the chocolate in a medium heatproof bowl and pour the hot cream over the chocolate. Let sit for 5 minutes, then stir until smooth. If using rainbow sprinkles, place them on a small plate.
Dip the tops of the orejas in the chocolate. If using rainbow sprinkles, lightly press the chocolate-dipped side into the sprinkles and return to the rack. Repeat with about half of the remaining cookies, leaving some plain, some chocolate dipped, and some dipped and with sprinkles.
Note: If you do not want to bake all of them at once, you may store the rolled oreja dough tightly wrapped in the refrigerator for a couple days, or freeze in a tight plastic bag for up to a month. Thaw in the refrigerator before baking.