Grilled Potato with capers

1 pound potatoes mini red and whites 1 x salt * 4 tablespoons olive oil divided 1 x black pepper freshly ground * Parsley pesto: 3 tablespoons pine nuts[...]

2 x Idaho baking potatoes , like russets peeled, sliced     into 12 pcs about 1/2"-thk, and     punched out with round cookie cutter 3 sm purple baking[...]