In the bottom of a steamer pot, put 4 cups water and 2 tablespoons salt. In the top portion of the pot, place the onions, fennel, potatoes and garlic. Pour the beer over the vegetables and add the sausage and 5 of the thyme sprigs. Bring to a boil over high heat, then reduce the heat to medium-high. Cover and steam for 15 minutes.
Then create layers, first by adding the corn, then the lobsters, followed by the clams and, finally, the remaining thyme sprigs. Cover and cook until the lobsters are bright red, the clams are open and the potatoes are cooked through, another 15 to 25 minutes.
Drain the liquid from the pot and reserve it in a bowl. Transfer the shellfish, sausage, potatoes, vegetables and corn onto a table covered with newspaper. Enjoy with melted butter, lemon wedges, crusty bread and the reserved broth.