Red Lentil Dal with Ghee and Spinach

Name: Red Lentil Dal with Ghee and Spinach
Ingredients: Dal; 6 tablespoons ghee or vegetable oil, divided.; 2 large onions, thinly sliced; 4 cloves garlic, minced; 2 tablespoons finely chopped peeled fresh ginger; 1 1/2 cups red lentils; 7 cups water; 1 1/2 teaspoons cumin seeds; 1 1/2 teaspoons good curry powder; 1 1/2 teaspoons salt; 1/8 - 1/4 teaspoons cayenne (to taste); a few handfuls baby spinach (or any other dark, leafy green, chopped if leaves are large); Ghee; 1 pound good unsalted butter