1 1/2 pounds small waxy potatoes no bigger than a small lime, halved
2 teaspoons fine-grain sea salt

1 tablespoon unsalted butter
2 tablespoons extra virgin olive oil
1 medium yellow onion, peeled and chopped
1 teaspoon whole cumin seeds
1 teaspoon curry powder
1/4 teaspoon turmeric
scant 1/2 teaspoon cayenne pepper
1 cup canned diced tomatoes
3/4 cup water
splash of cream or a dollop of creme fraiche

8 ounces tempeh, cut into 3/4-inch pieces
a small handful of cilantro, loosely chopped