Bring the water and salt to a boil in a medium saucepan. Sift the flour and baking powder together over a bowl. Add the flour mixture to the boiling water all at once. Stir with a wooden spoon until the mixture forms a ball and the sides of the pot are coated with a film.
Remove from the heat and let the batter cool for a couple of minutes. Transfer the batter to a bowl and using an electric mixer, beat in the egg yolks one at a time. Beat until very smooth.
Heat about 3 inches of oil in a saucepan to 350 degrees F. Put the batter in a pastry bag with a star tip. Pipe the batter into the hot oil. Fry until golden brown. Transfer to a paper towel-lined pan.
Mix the cinnamon and sugar together in a small bow. Sprinkle the churros generously with the cinnamon sugar. Serve warm.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.