Mix cinnamon and sugar on a large plate and set aside. Line tray with baking paper.
Heat water, sugar, salt, vanilla and butter in a saucepan over medium heat. Bring to boil then turn heat off and immediately add all flour.
Stir the flour vigorously with a wooden spoon until the dough forms a ball. Set it aside for a few minutes to cool down a little but pipe while stir warm and pliable.
Fit a large piping bag with a large closed star tip. Spoon dough into the bag and carefully pipe the hearts on the baking paper.
Heat oil in a large, deep pot. If you have a candy thermometer clip it on. The oil is ready when it reaches 190C | 375F.
Lower hearts into the oil using a wooden spoon. Do not fry more than 2 at a time as the oil temperature will drop. Flip and fry until golden - about 2-3 minutes on each side.
Drain on paper towels then roll in the cinnamon sugar.
To make the chocolate sauce, heat cream until just boiling then pour it over the chopped chocolate. Let it stand a couple of minutes then stir until chocolate is melted. Serve the churros plain or dip them in the chocolate sauce.