Cut the butter into thirds and bring it to room temperature.
Using 1/2 teaspoon shortening for each cup, grease the bottoms and sides of six 6-ounce custard cups or cups of a popover pan. Or, coat cups with nonstick cooking spray. Place the custard cups on a 15x10x1-inch baking pan; set aside.
In a medium mixing bowl use a wire whisk or a rotary beater to beat the 2 eggs, milk, and oil until combined. Add flour and 1/4 teaspoon salt; beat until smooth.
Fill the prepared cups half full with batter. Bake in a 400 degree F oven about 40 minutes or until popovers are very firm and golden brown.
Meanwhile, for the poached eggs, lightly grease a large skillet. Add water to skillet until half full. Bring water to boiling. Reduce heat to simmering (bubbles should begin to break the surface of the water).
Break one of the 6 eggs into a measuring cup. Carefully slide the egg into simmering water, holding the lip of the cup as close to the water as possible. Repeat with the remaining 5 eggs, allowing each egg to have an equal amount of space in the pan's water.
Simmer the eggs, uncovered, for 3 to 5 minutes or until the whites are completely set and the yolks begin to thicken but are not hard. Carefully remove the poached eggs with a slotted spoon, and place the eggs in a large shallow pan of hot water to keep them warm while preparing the sauce.
For Lime Hollandaise Sauce, in the top of a double boiler combine egg yolks, 1 tablespoon water, lime juice, and 1/8 teaspoon salt. Add a piece of the cut up butter. Place over boiling water (upper pan should not touch water). Cook, stirring rapidly with a whisk, until butter melts and sauce begins to thicken. Add the remaining butter, a piece at a time, stirring constantly until melted. Continue to cook and stir about 2 minutes more or until sauce thickens. Immediately remove from heat. If sauce is too thick or curdles, immediately whisk in 1 to 2 tablespoons hot water.
Immediately after removing popovers from oven, prick each popover with a fork to let steam escape. Turn off the oven. For crisper popovers, return the popovers to the still-warm oven for 5 to 10 minutes or until desired crispness is reached. Remove popovers from cups.
For each serving, split a popover in half and place on a plate. Top each popover with 1 slice of prosciutto. Top prosciutto with a poached egg; spoon about 2 tablespoons of the Lime Hollandaise Sauce over egg. Garnish with lime peel and serve with lime wedges, if desired. Makes 6 main-dish servings.