Melt butter, maple syrup, vanilla extract, and cinnamon over low heat. Once melted together, pull off the heat. Sift in powdered sugar, and whisk until fully combined. Allow to cool for 8-10 minutes so the glaze can thicken.
Once the glaze has thickened, give it a quick stir and pour it over the bread.
Allow the glaze to harden completely before cutting into slices.