Put cauliflower and cabbage with 1/2 cup water in a pressure cooker. Pressure cook to give one whistle. Keep on low flame for 5 minutes. Remove from fire
Grind ginger, garlic and green chillies to a paste
Heat 4-5 tbsp oil in a kadhai. Add chopped onions and cook till onions turn light golden
Add peas and cook covered till tender
Add prepared ginger paste and cook for 2-3 minutes on low flame
Add pao-bhaji masala and salt. Stir for a minute
Add tomatoes and cook covered for 5-6 minutes, stirring in between. Mash them well with a karchi so that the tomatoes blend well with the masala
Add pressure cooked vegetables and potatoes. Cook for 10 minutes, mashing them continuously
Add 4 tbsp butter and chopped coriander. Keep aside
To serve, cut buns into halves. Heat 1-2 tbsp butter in a pan or tawa and press the buns on the butter to make them turn golden and soft
Serve onions mixed in hari chutney alongwith the hot pao-bhaji and paos (buns)