Combine the Base Ingredients. In a blender, add 1 can (14 oz) of sweetened condensed milk, 1 cup heavy cream, 2 tablespoons chocolate syrup, 1 teaspoon vanilla extract, and a pinch (¼ teaspoon) of instant coffee granules (if using). Blend on low speed for 5–10 seconds until smooth.
Add the Whiskey. Slowly pour in 1 cup of Irish whiskey while blending on low speed to avoid curdling. Continue blending until the mixture is fully combined and creamy. Taste and adjust sweetness or chocolate flavor if desired.
Bottle & Chill. Transfer the mixture to a clean, airtight bottle or jar. Refrigerate for at least 1 hour to let the flavors meld. Shake gently before each use to maintain creaminess.