Preheat oven to 350Â°F.
In a heavy skillet, cook sausage meat while continually crumbling with a fork.
Remove sausage meat and drain well.
Add butter to sausage fat in skillet; saute onions until golden.
Remove onions with a slotted spoon and drain.
Cover pie shell with sausage meat and onions.
In a bowl whisk together eggs, cream, mustard and seasonings.
Stir in cheese.
Pour into pie shell and bake at 350Â°F for 35 minutes.