How to Make It
In a small saucepan, melt 1 tablespoon of the butter. Stir in the flour to make a paste. Gradually whisk in the milk until smooth and simmer, whisking, until the sauce thickens. Reduce the heat to low and cook, whisking, until no floury taste remains, about 5 minutes. Remove from the heat and whisk in the Gruyère and pimentón. Season the Mornay sauce with salt and pepper. Cover and keep warm.
In a large skillet, melt the remaining 1 tablespoon of butter in the olive oil. Add the shallot and garlic and cook over moderately high until softened, about 3 minutes. Add the spinach and cook over moderately high heat, tossing occasionally, until wilted, about 3 minutes. Season with salt and pepper.
Bring a large, deep skillet of water to a simmer. Crack the eggs into the skillet and simmer over moderately low heat until the whites are set and the yolks are runny, about 4 minutes. Using a slotted spoon, transfer the poached eggs to a plate; blot dry with paper towels.
Arrange 2 English muffin halves on each plate. Mound the spinach on the English muffins and top with the poached eggs. Spoon the Mornay sauce over the eggs and garnish with the chives. Serve right away.