In a small food processor pulse pecans until finely ground. Add 1/4 cup sugar and yolks and pulse until combined. Halve and pit nectarines and arrange, cut sides up, on a small baking sheet. Divide pecan mixture among nectarine halves, mounding it in center, and garnish each mound with a pecan half. Sprinkle nectarines with remaining tablespoon of sugar.
Bake stuffed nectarines in middle of oven until pecan mixture is golden, about 10 minutes. Serve nectarines with ice cream.