Add water, maple syrup, cocoa powder, cocoa butter, and salt to a small saucepan and bring to a boil over medium-high heat. Whisk to combine.
Reduce heat slightly and cook on a rolling simmer (~medium / medium-low heat) for 5 minutes until thickened, whisking occasionally. Then remove from heat and stir in vanilla.
Taste and adjust flavor as needed, adding more maple syrup for sweetness, saltiness for flavor balance, or cocoa powder for more intense chocolate flavor.
Use immediately as a hot chocolate sauce, or let cool completely and then store in a jar. It will thicken slightly in the refrigerator, which you can thin by adding in 1 Tbsp (15 ml) water or dairy-free milk at a time until desired consistency is reached.
*I use cocoa butter to keep this sauce naturally sweetened. However, feel free to sub bittersweet or dark vegan chocolate! Adjust amount of maple syrup as needed. *Recipe adapted from Food 52. *Nutrition information is a rough estimate.