Corned Beef Soup Under Cover

1 egg yolk 1/2 teaspoon dry mustard 1 pinch cayenne pepper 1 tablespoon water 1/2 cup butter , melted and warm (1 stick) 2 tablespoons lemon juice kosher salt[...]

6 slices bacon , cut crosswise into 1/4 inch pieces 1 1/4 cups onions , chopped fine 1 cup sliced carrot 6 russet potatoes , peeled and cut into 3/8 inch[...]