4 tablespoons unsweeted cocoa
2 cups powdered sugar
4 tablespoons unsalted butter, melted
1 cup hot water
1 teaspoon vanilla extract
1/8 teaspoon Kosher salt
Combine hot water, melted butter and vanilla extract in a small bowl.
Whisk together cocoa powder, powdered sugar and salt in a medium bowl.
Slowly pour liquid ingredients into dry ingredients, whisking continuously until smooth. Sauce will thicken as it cools.