Melt butter in a medium saucepan over medium heat. Add onion and garlic and saute until softened, about 6-8 minutes.
Add the ketchup, vinegar, worcestershire, liquid smoke, and brown sugar. Stir until fullly mixed and bring to a simmer. Add the tabasco and the molasses. Simmer 25-30 minutes, until sauce is a medium thickness. Season to taste with salt and pepper.
Let sauce cool for 1 hour, then puree until smooth in a blender. Serve warm or at room temperature.Store in an airtight container in the refrigerator.