Trim brisket. Brush with liquid smoke, celery salt, and pepper. Bake covered 3 to 5 hours at 275 degrees. (Place trimmed fat in bottom of baking dish.)

SAUCE:

Saute 1 onion, diced, in 1/4 cup butter.

Add:

1 1/2 c. water
1/2 c. lemon juice
1/4 c. vinegar
1/4 c. brown sugar
1 tbsp. dry mustard
1 tbsp. chili powder
1 tbsp. liquid smoke
2 c. catsup

Simmer covered 30 minutes. Salt and pepper to taste. Remove brisket from oven, slice across grain. Arrange slices in baking dish, add sauce and bake 30 minutes.