This is where your beef stock comes in—better yet, half beef/half chicken. Slowly cook a huge pile of very finely sliced onion in a good lump of butter and a jot of olive oil—low heat, 45 minutes, stirring frequently. Do not brown. When they are meltingly soft, add a good pinch of dried basil and grind on pepper. Glug in some dry white wine or vermouth, add stock and salt, and simmer a while to develop some flavor. Correct seasonings (a chef I once worked for added a shot of whiskey at this point). Ladle into crocks, float a hefty heap of grated gruyère on a raft of super-dry toast atop, broil, and enjoy.