Preheat the oven to a low temperature of 250 degrees F (120 degrees C) to create the perfect cooking environment.
Place the brisket in a large roasting pan, ensuring a disposable aluminum foil pan is suitable. Pour beer over the brisket, add onion sections on top, then season with garlic, salt, and pepper. Mix barbeque sauce, molasses, and liquid smoke together, then pour the mixture over the brisket. Cover the pan tightly with aluminum foil.
Preheat oven, then slow roast beef until fork tender. Rest for 10 minutes before thinly slicing across the grain. Enjoy!