To prepare sauce, combine 1 egg and the next 4 ingredients (through thyme) in the top of a double boiler. Cook over simmering water until thick (about 9 minutes), stirring constantly with a whisk. Remove from heat. Add butter, 1 piece at a time, stirring with a whisk until thoroughly incorporated. Keep warm.
To prepare Benedicts, remove the brown gills from the undersides of portobello mushrooms using a spoon; discard gills. Remove and discard stems. Cut mushroom caps into 1/2-inch-thick slices.
Heat a large skillet over medium-high heat. Add olive oil to pan; swirl to coat. Add mushrooms, and cook for 3 minutes on each side or until browned. Keep warm.
Bring a large saucepan of water to a boil. Add kale; cook 2 minutes or until just tender. Plunge kale into ice water; drain well.
Preheat broiler to high.
Place muffin halves, cut sides up, on a baking sheet. Broil 1 minute or until browned. Top each muffin half with 1 tablespoon cheese. Broil 1 minute or until cheese melts. Top cheese with one kale leaf; broil 1 minute. Top muffins evenly with mushroom slices. Keep warm.
Add water to a large skillet, filling two-thirds full. Bring to a simmer. Add vinegar. Break each egg into a custard cup, and pour gently into pan. Cook 3 minutes or until desired degree of doneness. Remove eggs from pan using a slotted spoon. Top each muffin half with 1 egg. Whisk sabayon over simmering water to reheat; spoon about 1 1/2 tablespoons sauce evenly over each egg. Sprinkle with pepper. Serve immediately.
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov.