Start by preheating the oven to 375F and greasing an 8" round baking dish.
Beat the eggs in a medium bowl. Add the shallot, mushrooms, milk, garlic, red pepper flakes, salf & pepper and whisk together until combined.
Pour the egg mixture into the baking dish. Top with the asparagus pieces and feta cheese.
Bake for 20-22 minutes until the middle is set. The edges may be puffed up, but as the frittata sets it will settle down.
Remove from the oven and allow to rest for 5-10 minutes. Serve immediately with any sides of choice. Enjoy!