Cheesy, Garlicy Au Gratin Potatoes

What goes better with ham than au gratin potatoes?    

7 c  Potatoes,Sliced Thin
4 ea Garlic,Minced
1/2 t  Dry Mustard
4 T  Butter
4 T  Cake Flour
1 c  Half And Half
3 c  Milk
2 c  Cheddar Blend
1/2 c  Parmesan

Wash potatoes and slice very thin.  Cover with water and set aside.

Heat oven to 350 degrees.  Butter a 2 quart casserole dish, set aside.

Melt butter in a large skillet.  Add garlic and mustard, cook until fragrant.  

Add flour and stir until mashed potato consistency.  

Add half and half, cook until thick.  

Add milk, one cup at a time, cooking until thick after each.  When all milk is added and thick, turn off heat and stir in cheeses until melted.  

Drain potatoes well, add to cheese.

Stir then pour into prepared pan.  

Bake at 350 degrees for 1 1/2 hours until potatoes are tender.