In a large sauté pan, heat butter. Add onions and garlic and sauté 2-3 minutes over medium high heat, until they are soft and fragrant.
Add potatoes, tomatoes, vegetable broth (or whey), curry powder and red pepper flakes. Stir to combine and bring to a simmer. Reduce the heat to medium and simmer 15-20 minutes, until the potatoes are tender and the sauce has reduced. (If the curry seems to be drying out too fast, add a little extra broth or whey.)
Stir in paneer cubes and serve warm with flatbread or rice.