In a small saucepan, whisk together 1/2 cup water, 1/2 cup granulated sugar, and 2 tablespoons corn syrup or honey. Set over medium heat and warm until the sugar dissolves and the mixture looks clear.

Whisk in 1/3 cup unsweetened cocoa powder and 1–2 teaspoons espresso powder until smooth. Keep the heat low to prevent scorching, and whisk continuously to remove any lumps.

When the mixture starts to steam and bubble lightly around the edges, remove from heat and add 3 ounces finely chopped dark chocolate. Let it sit for 30 seconds, then whisk until fully melted and glossy.

Stir in 1 teaspoon vanilla extract and 1/8 teaspoon fine sea salt. Taste. If you want it sweeter, whisk in another tablespoon of sugar while the sauce is still warm.

For extra silkiness, whisk in 1–2 tablespoons heavy cream or coconut cream (optional). This softens the bite and makes the sauce ultra-smooth.

Cool for 10–15 minutes. The sauce will thicken as it cools. Transfer to a clean glass jar or squeeze bottle.

To use: stir 1–2 tablespoons into hot coffee or espresso, or shake with iced coffee before adding ice. Adjust to taste.