Heat a 12” cast iron skillet over medium high heat. Add the oil and butter to the skillet and heat until the butter foams then subsides.
Add the potatoes and a pinch of salt to the skillet, and stir to coat in the fat. Saute the potatoes, stirring occasionally, until barely tender, 20 minutes. You should be able to insert a knife tip into a potato easily, but still see a bit of crumbling/resistance in the flesh. The potatoes will continue to cook in the following steps, so take care not to overcook them at this stage.
Add the canadian bacon. Toss to incorporate with the potatoes and fat, and saute until the bacon is lightly browned, 5 minutes.
Add the spinach to the skillet. Saute, tossing frequently, until the spinach is wilted, 2-3 minutes.
Turn off the burner heat. With a wooden spoon distribute the hash throughout the pan in an even layer. Then, make 7 depressions evenly spaced throughout the skillet. Gently crack an egg and pour the egg into each depression.
Transfer the skillet to the oven and bake until the egg whites are just set, 7-8 minutes.
Remove the casserole from the oven and sprinkle with additional salt and cracked black pepper. Drizzle the hollandaise sauce over the casserole, garnish with fresh parsley, and serve immediately. This casserole makes seven generous servings. It doesn’t reheat well, and leftovers are best eaten the same day.