Heat the oven to 375°F and butter a 9-by-13-inch dish. Brown the sausage in a skillet for 8 minutes, breaking it into pea-size pieces and cooking it to 160°F; drain.
Whisk the flour, sugar, baking powder, baking soda and salt in a bowl. Whisk the eggs, buttermilk and melted butter in a second bowl.
Fold the wet mixture into the dry just until flour disappears; leave small lumps. Fold in the sausage and spread in the dish.
Bake for 25 to 30 minutes, until the middle springs back and a toothpick comes out without wet batter.
Rest for 5 minutes, cut into eight squares and divide the maple syrup among the servings.