Cauliflower Taco Bake

INGREDIENTS
FOR THE BEEF
1 tbsp. extra-virgin olive oil
1/2 yellow onion, diced
2 lb. ground beef
Kosher salt
Freshly ground black pepper
2 tbsp. keto taco seasoning mix
4 large eggs, lightly beaten
FOR THE CAULIFLOWER
Kosher salt
1 small head cauliflower, cut into small florets
FOR THE CHEESE SAUCE
4 oz. cream cheese
2/3 c. heavy cream
2 tbsp. butter
1/2 tsp. ground mustard
1/4 tsp. garlic powder
3 c. shredded cheddar, divided
Kosher salt
1/4 c. sliced green onions

DIRECTIONS
Preheat oven to 350°. Make beef: In a large skillet over medium, heat oil. Add onion and cook until slightly softened, 2 minutes. Add ground beef and season with salt and pepper. Cook, breaking up meat with a wooden spoon, until no longer pink, 6 minutes. Drain excess fat and sprinkle in taco seasoning, stirring to coat meat. Remove from heat and let cool slightly.
In a medium mixing bowl, whisk eggs, then stir in meat mixture. Spread mixture into an even layer in the bottom of a 9″-x-13″ baking dish.
Meanwhile, make cauliflower: In a large pot of salted boiling water, blanch cauliflower, 3 minutes. Drain and squeeze water from cauliflower. Arrange cauliflower in an even layer on top of beef in baking dish.
Make cheese sauce: In a medium saucepan, combine cream cheese, heavy cream, butter, ground mustard, and garlic powder, and cook over medium, stirring constantly, until melted and smooth. Remove from heat and whisk in 2 cups cheddar until smooth. Season with salt and stir in green onions.
Pour cheese sauce over cauliflower in baking dish and top with remaining 1 cup cheddar. Bake until cauliflower is tender, beef is set, and cheese is melty, about 30 minutes. If desired, broil until golden, about 2 minutes.