Remove seeds from cardamom pods. In a dry small skillet over medium heat, toast the cloves and the fennel, cumin, coriander, mustard and cardamom seeds until aromatic, about 1-2 minutes. Cool.
Transfer to a spice grinder or a mortar and pestle (in batches if necessary); grind until mixture becomes a powder. Stir in the turmeric, salt and cayenne.
In a large bowl, combine oil and spice mixture. Add potatoes; toss to coat. Arrange in a single layer in an ungreased 15x10x1-in. baking pan. Bake at 425° for 16-20 minutes or until golden brown, turning once.
Meanwhile, combine yogurt and mint in a small bowl. Serve with potatoes.