1. In a large pot or Dutch oven, heat butter and oil over medium heat. Add shallots, thyme, and garlic; cook until shallots begin to soften, about 3 minutes. Add beer, and bring to a simmer. Add clams and mussels; return to a gentle simmer.
2. Cover pot with a lid, and reduce heat to medium-low. Cook until shells open, about 10 minutes. Discard unopened shells. Serve with lemon wedges and a bowl for the shells.