First, make the hollandaise: Add the egg yolks to a blender with the lemon juice and a pinch of salt. Blend on high for 30 seconds, until totally mixed. Adjust the blender speed to low and slowly drizzle in the hot melted butter. The sauce will start to get very thick. Add the mustard, black pepper and cayenne and mix until combined. If it becomes too thick to blend, squeeze in the juice of the other half of the lemon and try again. Put the lid on the blender and keep warm.
Crack the eggs into separate small ramekins. Set aside.
In a large nonstick skillet, cook the bacon over medium-high heat, turning until crisp. Remove from the skillet and drain on a paper-towel-lined plate. Pour off the grease, reduce the heat to medium-low and add the garlic. Stir and cook for 30 seconds, being careful not to burn the garlic. Add the kale, sprinkle with salt, pepper and red pepper flakes. Cook for about 3 minutes, until the kale is wilted. Set aside and keep warm.
To poach the eggs, boil 2 quarts of water in a medium saucepan over medium-high heat. Add a pinch of salt and the vinegar. Use a metal spoon to carefully stir a vigorous "whirlpool" in the water. Immediately drop 2 of the eggs into the center of the whirlpool and let them cook for about 3 minutes for a soft yolk. Use a slotted spoon to carefully lift the eggs out of the water. Gently shake the spoon and check the doneness. If they are too soft, return them to the water for 45 seconds. Repeat with the other eggs. Drain on a paper-towel-lined plate.
Place some of the kale in a neat pile on 4 plates. Top with bacon, then place the eggs on top of the bacon.