In a heavy mixing glass, combine the toasted marshmallow syrup, chocolate bitters, and bourbon.

Fill the mixing glass three-quarters full with solid ice cubes.

Using a long bar spoon, stir the cocktail smoothly for thirty seconds until chilled.

Place one large clear ice cube into a double old fashioned glass and strain the liquid directly over it.

Garnish with toasted marshmallows resting across the rim on a bamboo skewer and serve immediately.

Combine Sugar and Water: In a small saucepan over medium heat, combine 1 cup of sugar and 1 cup of water. Stir occasionally until the sugar is completely dissolved and the liquid comes to a gentle simmer.

Melt in the Marshmallows: Add the warm, toasted marshmallows directly into the simmering syrup. Lower the heat to medium-low and whisk continuously for 3 to 5 minutes until the marshmallows fully dissolve into the liquid.

Add Vanilla & Strain: Remove the pan from the heat and stir in 1 teaspoon of pure vanilla extract. Strain the syrup through a fine-mesh sieve into a bowl or jar to remove any undissolved gelatin foam or heavy char bits.

Cool & Bottle: Allow the syrup to cool completely at room temperature before pouring it into a clean glass bottle or airtight jar.