Step #1 In a small bowl, with a fork, mix butter & 1 tbsp mustard.
Step #2 Combine wine & shallots in a 1 1/2- to 2-quart pan; stir often over medium-high heat until liquid is almost evaporated, 5 to 6 mins.
Step #3 Whisk in cream & remaining 1 tbsp mustard.
Step #4 Simmer, stirring often, until sauce is reduced to 1 c & is thick enough to coat spoon in a velvety layer, 8 to 10 mins.
Step #5 Add salt & pepper to taste.
Step #6 Meanwhile, in a 5- to 6-quart pan over high heat, bring 4 inches of water to a boil.
Step #7 With a slotted spoon, immerse each whole egg in water for 10 seconds.
Step #8 Lift out.
Step #9 Pour out all but 1 inch water; reduce heat so bubbles on pan bottom pop to the surface only every once in awhile.
Step #10 Spread 1 1/2 tsps mustard butter on one side of each slice of bread.
Step #11 Lay, buttered side down, on a griddle or in two 10- to 12-inch frying pans over medium-high heat; spread remaining butter mixture over tops of slices.
Step #12 When bottoms are lightly browned, in about 3 mins, turn slices over.
Step #13 Top equally with cheese.
Step #14 Reduce heat to medium.
Step #15 One at a time, crack eggs and, holding close to surface of water, break open & let egg slide in.
Step #16 Cook to desired doneness (poke with a spoon to check), 4 mins for soft yolks.
Step #17 When cheese on sandwiches begins to melt, in 2 to 3 mins, top this with prosciutto; cook this until warm, about 2 mins.
Step #18 Mound salad mix on plates.
Step #19 Transfer a sandwich to each mound.
Step #20 With a slotted spoon, lift poached eggs from water & set two on each sandwich.
Step #21 Ladle mustard-wine sauce over eggs.
Step #22 Serve as soon as possible, adding more salt & pepper to taste.
Step #23 Notes: The mustard butter & mustard-wine sauce (steps 1 & 2) can be made up to 1 day ahead; cover each & chill in the fridge.
Step #24 Warm sauce over low heat/flame or reheat in a microwave oven at full power (100%), stirring every once in awhile, to use.
Step #25 Garnish sandwiches with fresh chive spears.
Step #26 Nutritional analysis per sandwich.
Enjoy the Prosciutto & Poached Egg Sandwiches with Mustard-Wine Sauce recipe