In a saucepan combine the butter and the flour and cook the roux over low heat, stirring, for 3 minutes. Whisk in the beer and the tomatoes and boil the mixture, whisking, for 3 minutes. Reduce the heat to moderately low, stir in the Cheddar, the mustard, the Worcestershire sauce, and the Tabasco, and cook the mixture, stirring, until it is hot (but do not let it boil). Arrange 3 of the toasts or 2 of the muffin halves on each of 6 plates and spoon the Cheddar mixture on top. Garnish the Welsh rabbit with the parsley and serve it with the bacon. Serves 6. Gourmet October 1990