1/4 cup butter, softened
1/2 teaspoon seasoning salt
2 tablespoons Dijon mustard
1/4 cup chopped onion
1 1/2 pounds beef brisket
1 pound Swiss cheese
1/2 cup mayonnaise
1 1/2 cups Dijon mustard
1/4 cup olive oil
Preheat oven to 350 degrees F (175 degrees C).
In a medium saucepan, combine butter, seasoning salt, mustard, onion and beef. Stir constantly over medium heat until it is browned.
Place Swiss cheese in a 9x13 inch baking dish. Pour mayonnaise over cheese and spread evenly. Arrange meat mixture over Swiss cheese. Top with mayonnaise.
Pour Dijon mustard over the entire meat and cheese mixture. Sprinkle with olive oil. Cover tightly and bake in preheated oven for 50 minutes.