Add butter to saucepan, and melt over medium. Whisk in flour; cook, whisking constantly, 1 minute. Gradually whisk in milk. Bring to a boil over medium, whisking occasionally. Boil, whisking occasionally, until slightly thickened, about 2 minutes. Stir in parmesan cheese, pepper and salt. Add potatoes. Cook, stirring constantly, until potatoes start to break apart and mixture is thickened, about 2 minutes. Add in the blanched sugar snap peas and stir until they are hot. Sprinkle with chives and serve immediately.