Preheat oven to 375°F.
Melt butter in a small saucepan over medium heat; stir in flour and ½ teaspoon salt. Whisk constantly for 2-3 minutes or until it starts to bubble and brown.
Add cream and stir constantly for 3 minutes until the sauce starts to thicken.
Add 4 ounces cheddar cheese to pot and heat for another minute and stir to combine until the cheese is melted and incorporated.
Put olive oil, broccoli and remaining salt in a cast iron skillet over medium heat. Sauté for 3 minutes.
Add pierogies and sauté for an additional 5 minutes.
Add cheese sauce to skillet and sprinkle with the remaining cheese and breadcrumbs.
Put skillet in oven and bake for 10-15 minutes until crispy and brown on top.
