In a small baking dish, whisk together sugar and ground cinnamon until combined. Set aside.
In a saucepan, add the water, butter, and salt. Stir to combine, at medium-high heat, until the butter has melted. Once the butter has melted, reduce heat to low.
Add the flour and mix with a spatula until a dough forms. Remove from the heat, transfer the dough to a bowl and let it cool down.
In a bowl or in a stand mixer, whisk the eggs into the dough, one by one, until the dough is smooth. The dough may look crumbly but keep going. It will smooth out eventually.
In a large saucepan, heat oil at medium heat until it reaches 325ºF.
While the oil heats up, spoon the dough into a large piping bag with a star tip.
Pipe out 6-inch strips of dough into the hot oil and fry until golden brown, about 1-2 minutes on each side. I used a scissor to cut the dough as I piped them into the hot oil. Be careful when you do this and make sure you don't crowd the pan with too many. I did about 3-4 at a time. Drain them on a paper towel lined plate then toss in cinnamon sugar.
Once the churros have cooled, you can serve them as is, with Spanish Hot Chocolate, or dip them in dulce de leche. Enjoy!