Slow Cooker Sunday Gravy

1 small onion, diced (about 1 cup) 1 carrot, grated on the large holes of a box grater 1 1/4 pounds cubed chuck steak Kosher salt and freshly ground black pepper 6 cloves garlic, chopped 1 whole sprig fresh basil, plus 1/2 cup leaves, torn 1/4 cup dry red wine, optional 1 tablespoon tomato paste 2 teaspoons all-purpose flour Two 15-ounce cans no-salt-added crushed tomatoes 12 ounces whole-wheat penne or similar shaped pasta