Preheat oven to 350 degrees. Butter a baking dish (or use non-stick
cooking spray). In a saucepan, melt 2 tablespoons of the butter over
medium high heat. Stir in flour and cook for 1 minute. Remove saucepan
from heat and whisk in milk and onions. Return pan to heat and bring to
a simmer while stirring. When sauce has thickened remove from heat, add
the cheese and stir until the cheese has melted and sauce is creamy.
Remove from the heat and stir in the ham.
Taste for salt (some ham will have enough salt and no additional
will be needed). Peel and slice the potatoes and add half of the
potatoes to the buttered casserole dish. Evenly pour half of the cheese
and ham mixture over the potatoes. Add the remainder of the sliced
potatoes and finish with the rest of the sauce, making sure to
distribute it evenly. Season with black pepper over the top.
Melt the remaining butter in a small non-stick skillet and add the
panko crumbs. Sauté just until the crumbs begin to brown and remove from
the heat. Sprinkle the crumbs evenly over the potatoes and bake for 45
minutes at 350 degrees or until golden brown and bubbly.