Place pecans in a single layer in a shallow baking dish; sprinkle with salt, and dot with butter. Bake at 350° for 5 minutes. Remove from oven, and toss lightly. Return to oven, and bake an additional 5 minutes. Set aside to cool.
Combine sugar, cornstarch, syrup, and eggs in top of a double boiler. Gradually add milk, stirring until well blended. Place over boiling water and cook, stirring constantly, until mixture thickens. Remove from heat, and cool to room temperature; chill thoroughly. Stir in half-and-half, vanilla, and reserved pecans.
Pour mixture into freezer can of a 2-quart hand - turned or electric freezer. Freeze according to manufacturer's instructions. Let ice cream ripen at least 1 hour before serving. Spoon into individual bowls or parfait glasses, and serve immediately.