To make the dough for the churros, heat the water, butter & salt to a rolling boil in a saucepan. Next add the flour, stirring it for about a minute or so. Beat your eggs until they're smooth then add them into the mixture, too. Next, you'll need to spoon the mixture into a piping bag that has a star shaped nozzle- about 10cm each. Fry them in a saucepan- about 3 or 4 at a time until they're golden brown. Put them aside on a paper towel then roll them in the sugar. For the hot chocolate, pour the milk and cornstarch into a saucepan and whisk until the cornstarch dissolves. Once it does, heat the milk until it boils, then remove the heat or keep it on very low. Start adding chocolate immediately and stir until the chocolate is completely melted. As soon as you get a thick mixture remove it from the heat and serve!