Preheat the oven to 400°. F
In a medium saucepan cook the egg noodles and drain and set aside.
Cube your ham and set aside.
In a medium saucepan, over medium heat, melt butter.
Add the minced onion and cook until transparent. (2 or 3 minutes)
Add the flour, making a roux Stir constantly with a wooden spoon until blended. Do not let the roux turn brown.
When the roux is white and bubbly add the milk slowly, stirring to mix thoroughly.
Add the seasoning salt, celery salt, pepper, and Worcestershire sauce.
When the mixture starts to bubble, but not boil add the cubes of Velveeta cheese. ..
Keep stirring regularly until the cheese is melted and is a nice thick sauce. Remove from the heat.
In a 9" x 13" baking dish alternate the ham, noodle, corn, and sauce, mixing well after each addition until it is all thoroughly mixed. Smooth out the top.
Bake at 400°.F for 15 minutes and then reduce the temperature to 350°.F. Bake for another 30 minutes.