Step 1

Heat oil in a large nonstick skillet over medium-high. Add bacon. Cook, stirring often, until lightly browned, about 4 minutes. Remove bacon with a slotted spoon to a paper towel-lined plate, reserving drippings in skillet. (Do not wipe skillet clean.) Return skillet to medium-high. Working in batches, add English muffin halves, cut sides down, to hot drippings in skillet. Cook until toasted, about 1 minute. Let muffin halves cool slightly.

Step 2

Chop English muffin halves into bite-size pieces. Place on bottom of a lightly greased (with cooking spray) 13- x 9-inch baking dish. Sprinkle with cooked bacon. Finely chop white parts of scallions, and sprinkle over mixture in dish. (Wrap green parts of scallions in a damp paper towel; chill until ready to use.) Whisk together whole eggs, milk, pepper, and 1 teaspoon of the salt in a large bowl. Pour over mixture in baking dish; cover with plastic wrap. Chill at least 8 hours or up to 16 hours.

Step 3

Preheat oven to 350ºF. Let casserole stand at room temperature while oven preheats. Bake until top is browned and casserole is set, about 40 minutes.

Step 4

Meanwhile, make hollandaise. Melt butter in a small skillet over medium-low. Keep butter hot over lowest heat (do not let it brown). Process egg yolks, lemon juice, mustard, paprika, and remaining 1 teaspoon salt in a blender on medium just to combine, about 5 seconds. With blender running on medium speed, slowly pour hot, melted butter through center opening in blender lid. Process until mixture is smooth and thick, about 1 minute.

Step 5

Drizzle about ½ cup hollandaise over warm casserole. Finely chop reserved green scallion parts, and sprinkle over top. Sprinkle with paprika; serve with remaining hollandaise.