In a saucepan over medium low heat, melt 1 Tbsp of unsalted Butter, add in the All Purpose Flour, stirring to form a paste.
Add about 1 Tbsp of the Milk and mix well, once incorporated add remaining Milk and continue to cook, stirring continuously to keep from scorching.
Stir in the Dijon Mustard and Nutmeg, mixing well.
Mix in the grated Cheese, mixing well and continuously stirring until thickened and well combined. Set aside.
Preheat oven 350°F. Use a non-stick spray to grease a muffin pan.
Remove the crust from the Bread and roll out with a rolling pin.
Melt the Butter and spread over the Bread slices on both sides. Place each piece in a muffin cup, gently pushing the bread down to form a cup.
Into each Bread cup layer with the Prosciutto (I half each slice, which fits best into the bread cup).
Add one Egg to each cup, pouring off any Egg white if needed to make room. Top off with the Mornay Sauce (1 - 2 Tbsp per cup),
Season with Salt & Pepper, to taste. Bake in a preheated 350°F oven for 15 - 20 minutes. Less time needed for a runnier yolk.
Garnish with more grated cheese, chopped Flat Leaf Parsley, if desired, and season with Salt and Pepper, to taste.