In a large bowl, combine ground beef, onion, garlic, tomato paste, tomato, egg, pepper flakes, oregano, basil, sage, pepper & salt until well incorporated. Set aside.
Remove the whole stem from the cauliflower making sure to leave the head fully intact. In a large pot, boil cauliflower for 8-10 minutes until fork tender. Remove from the boiling water & place on paper towels to drain for a few minutes then carefully remove any remaining stem to make space for the filling.
Preheat oven to 400 F. Fill the head of cauliflower with ground beef mixture making sure to press the filling into the head. Place inverted head of cauliflower on a buttered, foil lined baking sheet; cover with another sheet of foil & bake about 30 minutes or until beef is cooked through.
Cheese Sauce
In a saucepan, melt butter add flour, stirring until light brown, about 2 minutes. Stir in milk & allow to thicken, about 5 minutes. Add grated cheese, salt & pepper & mix until fully incorporated & thickened.
Adjust heat to broil. Remove foil from stuffed cauliflower & cover with cheese sauce. Broil about 5 minutes or until lightly browned. Garnish with fresh parsley.