Preheat the oven to 350 degrees F.
Smush the softened butter with a fork. Dump in the sugar, cinnamon and vanilla. Stir to completely combine. Spread the mixture on the bread slices, completely covering the surfaces all the way to the edges.
Place the bread on a baking sheet and bake for 10 minutes. Turn on the broiler and broil until golden brown and bubbling. Watch so it doesn't burn!
Cut the slices into halves diagonally and serve.