Preheat your oven to 180ºC (350ºF). While the oven heats, gather your baking dish and other ingredients.

Toss the cubed potatoes with olive oil and salt until coated. Spread in a single layer on a baking sheet and roast for about 30 minutes, stirring halfway through.

Heat a skillet over medium heat and cook the chopped bacon until crispy, about 5-7 minutes. Add the chopped onion and cook until softened, about 3-4 minutes, then stir in crushed garlic for the last minute.

Transfer the roasted potatoes to a greased casserole dish. Add the bacon and onion mixture along with half of the cheddar cheese. Mix everything together.

In a mixing bowl, whisk together eggs, milk, heavy cream, and pepper. Pour this mixture over the potato and bacon layers.

Sprinkle the remaining cheddar cheese on top. Bake for 30-40 minutes, or until puffed, set, and golden brown.

Let the casserole rest for 5-10 minutes before slicing and serving.