Preheat oven to 400°F (200°C).
Boil potatoes until fork tender. Drain well and let steam dry.
Transfer the potatoes to a greased springform pan. Using the bottom of a measuring cup or a meat tenderizer, press them firmly into the bottom and up the sides to create an even crust.
Brush with olive oil and season with salt and pepper.
Bake for 40–45 minutes until golden and crispy.
Reduce oven to 350°F (175°C).
Whisk together eggs, milk, heavy cream, garlic powder, and salt.
Stir in chopped onions, broccoli, and shredded cheddar.
Pour into the baked crust.
Top with mozzarella and more cheddar.
Bake for 50–55 minutes, until the center is just set.
Rest for 15–20 minutes before slicing and serving.
