1. Sift the flour and baking powder into a bowl and set aside. Bring the measured water to a boil in a saucepan, add the salt and brown sugar, stirring constantly, until both have dissolved. Remove from heat, add all the flour and baking powder and beat the mixture continuously until smooth.
2. Beat in the egg yolks, one at a time, until the mixture is smooth and glossy. Set the batter aside to cool. Have ready a piping bag fitted with a large star nozzle, which will give the churros their traditional shape.
3. Pour oil into a deep-fryer or suitable saucepan to a depth of about 2 inches. Heat to 375F, or until a cube or dried bread, added to the oil, floats and turns golden after 1 minute.
4. Spoon the batter into the piping bag. Pipe five or six 4-inch lengths of the mixture into the hot oil, using a knife to slice off each length as it emerges from the nozzle. Fry for 3-4 minutes or until they are golden brown. Drain the churros on paper towels while cooking successive batches, then arrange on a plate with the lime wedges, dust them with sugar and serve warm.
