In a small pot, melt 10 tbsp. butter; cook until hot but not boiling. Set melted butter aside; keep warm. Add yolks of 3 eggs, lemon juice and salt to a blender; blend on medium-high speed until mixture lightens in color (about 30 sec.). Reduce blender speed to low. Slowly drizzle in hot melted butter; continue to blend on low for several seconds after butter is fully incorporated. Cease blending and adjust lemon juice and salt to taste. Add hot water 1 tsp. at a time, pulsing in between to blend, until desired consistency is reached. Transfer sauce to the pot used to melt the butter; keep warm over very low heat until needed. In a large sauté pan, heat olive oil over medium heat. Add spinach; cook until spinach is wilted (about 1 min.). Evenly top bagel halves with spinach. Add ham to sauté pan; cook until hot (about 1 min.). Place 2 slices ham atop spinach on each bagel half. Melt remaining butter in sauté pan until foam subsides. Crack remaining eggs into pan; cover and cook until whites are just set and yolks are still runny (about 3 min.). Add 1 egg to each bagel stack; drizzle with sauce to taste. Serve immediately with salt and pepper at the table for passing.
- Poached eggs are a delicious alternative to the fried eggs called for in this recipe.