Line the bottom and sides of a greased 15-in. x 10-in. x 1-in. baking pan (jelly roll pan) with parchment paper; grease the paper and set aside.
In a small bowl, beat cream cheese and slowly add milk until smooth. Add flour and salt; mix until combined. In a large bowl, beat the eggs until blended. Add cream cheese mixture; mix well. Pour into prepared pan.
Bake at 375° for 30-35 minutes or until eggs are puffed and set. Remove from the oven and use parchment paper to remove egg from the pan.
Immediately spread with mustard and sprinkle with 1 cup cheese. Sprinkle with ham, onions and 1 cup cheese. Roll up from a short side, peeling parchment paper away while rolling.
Sprinkle top of roll with the remaining cheese; place back on baking pan bake 3-4 minutes longer or until cheese is melted. Yield: 12 servings.