In a non-reactive saucepan, melt the butter over medium-low heat. Add the onion and garlic and cook until just beginning to develop color, about 10-12 minutes.
Add in the can of Pennsylvania Dutch Birch Beer along with the remaining ingredients. Stir slowly and constantly with a wooden spoon until the Birch Beer BBQ sauce is smooth and well combined.
Simmer uncovered for 25-30 minutes, stirring occasionally until the sauce begins to thicken. Adjust seasonings to taste.
Remove from heat and allow the Birch Beer BBQ sauce to cool for 10-15 minutes. Using a "stick" or immersion blender, puree the sauce until reaching a smooth, thickened consistency.
Important: Hot liquids expand when blended. If using a traditional blender, work in small batches. Be sure to allow for venting. Remove your blender's lid vent plug and cover the opening with a clean kitchen cloth.
Cool the sauce to room temperature, then use as desired, Use a BBQ sauce mop or the back of a large spoon to apply the PA Dutch Birch Beer BBQ Sauce to pork, chicken or beef.
Apply sauce liberally and continue cooking/grilling for 5 minutes. Reapply a light coating of Birch Beer BBQ Sauce then continue cooking for another 5-10 minutes before serving.
Store unused PA Dutch Birch Beer BBQ Sauce in the refrigerator. Brush it on food 5 to 15 minutes before the cooking time is finished. If desired, serve extra on the side.