For the dough: In a small saucepan, combine the milk, butter and salt and bring to a medium heat. When the butter has melted, add the flour and whisk to combine. Switch over to a wooden spoon and cook the dough until it pulls away from the sides of the pan and it has a slightly sweaty sheen on it, 3 to 4 minutes.
Transfer the dough to a mixing bowl and let cool for 2 to 3 minutes. Using an electric mixer beat in the eggs 1 at a time. Do not add the next egg until the last one is completely combined.
Place the batter in a pastry bag outfitted with a large star tip. Reserve.
To make the chocolate sauce: Place 1-inch of water in a small saucepan and bring to a boil.
In a heatproof mixing bowl, combine the chocolate, heavy cream, butter and corn syrup. Heat, stirring occasionally, until the chocolate is melted and all the ingredients are well combined.
Cover the bowl with plastic wrap and remove the saucepan from the heat. Reserve.
For the cinnamon sugar: In a bag or large mixing bowl, combine the sugar and cinnamon
In a large saucepan heat the oil to 325 degrees F.
Pipe the dough into the hot oil in sticks or desired shapes (I kinda like to make mine a little curly). This might be a little tricky at first, but you'll get the hang of it. Fry the dough until it is brown and crispy on all sides, 60 to 90 seconds total, turning frequently. Fry in batches.
Remove the churros from the oil, blot on paper towels for a second and then toss in the cinnamon sugar. Be sure to do this while the churros are still hot. Serve immediately, while churros and melted chocolate are warm.