Measure 15 3x5 rectangles on parchment paper and cut them to size. Set aside.
In a medium saucepan, heat butter, sugar, salt, and water together over medium-high heat until it boils. Immediately add all of the flour and stir with a wooden spoon. Continue to stir over heat until a firm forms on the bottom of the pan. Remove from heat and transfer dough to a medium bowl to cool down for 3 minutes.
Once slightly cooled, add 1 egg to dough and stir vigorously until combined into dough. Repeat with rest of eggs, one at a time.
Transfer mixture to a large pastry bag fitted with a large star piping tip. Spread out all 15 rectangles of parchment paper. Slowly pipe a loop onto a prepared rectangle of parchment paper. Repeat on all rectangles of parchment. In a large Dutch oven, heat about 3 inches of oil over medium heat. Add a candy thermometer to monitor the oil temperature. Once the oil reaches 375°F, it’s ready for frying.
Slowly place one rectangle with piped dough into hot oil. Place another right next to it. Do not add more than 2 at a time. Let the dough cook with the parchment for 30 seconds or until you can gently slide off the parchment. Discard parchment paper. Keep cooking for 2 minutes, flip, and cook for 2 minutes longer. Monitor the oil temperature to ensure it doesn’t go lower than 350°F or higher than 385°F. Remove the cooked churros and drain them on a plate lined with paper towels. Repeat the process until all the dough has been fried.
Place the sugar to a shallow bowl. Toss the churros to coat in the sugar, no more than 2 at a time.