Delicate, lace-like buñuelos shaped on molds and fried are a skilled Mexican tradition. This family dessert is a crispy, artistic, sweet confection of holiday celebrations.
In a medium bowl, whisk the flour, salt, milk, egg, melted butter, and vanilla extract until the batter is smooth and slightly runny.
Pour vegetable oil into a deep, heavy pan to a depth of at least 2 inches. Heat oil to 370°F (188°C) over medium-high heat, checking temperature with a thermometer.
Place the buñuelo mold in the hot oil for 1 minute to preheat, ensuring the batter won’t stick when dipping.
Dip the hot mold into the batter, only covering the bottom and sides (don't let batter come over the top), then immediately submerge in hot oil. Fry until golden and crisp, about 45–60 seconds, gently shaking to release the buñuelo.
Transfer fried buñuelos to a paper towel-lined plate to drain. While still hot, dust generously with cinnamon sugar. Repeat for remaining batter, reheating mold as needed. Serve warm or cooled.