Preheat the oven to 400°F (200°C).
Fry the ground beef in butter over medium high heat until cooked through and no longer pink.
Add Tex-Mex seasoning and crushed tomatoes. Stir and let simmer for 5 minutes. Taste to see if it needs additional salt and pepper.
Place the ground beef mixture in a greased baking dish (about 9" or 23 cm in diameter). Top with jalapeños and cheese.
Bake on upper rack in oven for 15–20 minutes or until golden brown on top.
Mix the scallion with the crème fraîche or sour cream in a separate bowl.
Serve the casserole warm with a dollop of the sour cream. guacamole and a green salad.