Step 1: Fry garlic, cumin, mustard, fenugreek and pepper in a pan. Let these spices pop.
Step 2: Then add green chili paste, ginger paste, tumeric, salt, and coriander powder. Stir and sizzle for another few seconds.
Step 3: Now add chopped onions. Fry onions till they get soft. (3-4 minutes)
Step 4: Add chopped tomatoes and dried fenugreek leaves. Simmer the gravy for 5 minutes. Chop spinach while gravy sizzles.
Steps 5: Now most of tomato water has dried and you should a see little oil in the sides of pan.
Step 6 and 7: Add potatoes and chopped spinach to gravy and cover the pot without stirring for 5 minutes. Let the spinach get soft. Now you can easily mix it well. Cover again and cook till spinach and potatoes are tender. (15 minutes).
Step 8: Add butter and dry water on high heat till you see oil on the sides of pan. (bhunna) 2-3 minutes.
Garnish with sliced green chilies and serve with plain yogurt or raita.