In a large mixing bowl, whisk together the flour, baking powder, salt, and ground cinnamon until well combined. In a separate bowl or measuring cup, whisk together the milk, cooled butter, vanilla extract, and egg until well combined. Pour the wet ingredients into the dry ingredients and stir together with a wooden spoon until a soft dough forms. Place the dough on a lightly floured surface and knead a few times until the dough forms a smooth, slightly elastic ball.
Cut the dough into 10 equal portions and roll each into a round ball. Working with one ball of dough at a time, on a lightly floured surface roll the dough out into a thin tortilla, about 7-inches across. As each tortilla is rolled out, lay them on a cooling rack to allow them to dry a little before frying. This drying step really did give the finished bunuelos a much crispier texture.
Once all the bunuelos are rolled out and draped on the cooling rack, pour enough oil in a large skillet to cover the bottom of the skillet to a depth of about 1 inch. Heat the oil over medium heat until it is shimmering and hot. While the oil heats, prepare the sugar topping by stirring together the 1/2 cup sugar and ground cinnamon. Line a sheet pan or large tray with paper towels for draining the cooked bunuelos.
Place one bunuelos in the hot oil and allow it to cook for about 1 minute on each side, or until both sides are golden brown and the dough is bubbly. I found it was helpful to press down on the center of the dough after putting it in the skillet as it tends to bubble up in the center leaving the center dough under-cooked. After the bunuelos is crisp and golden brown on both sides, remove it to the paper towel lined baking sheet or large tray to drain. Repeat with remaining discs of dough. Sprinkle each bunuelos with the cinnamon sugar mixture while it is still warm. Serve immediately, while still warm if possible!
Serving Size 1 piece