Fill a medium saucepan halfway with water, cover, and bring to a boil. Uncover, add 1 tbsp salt and pasta, and stir for a few seconds. Cook until desired firmness, 8-10 minutes.
Wash asparagus, snap off woody ends, and cut diagonally into 2 inch (5 cm) pieces. Add to pasta during the final 2-3 minutes of cooking time. Boil until bright green and tender-crisp.
Wash lemon and grate 1 tsp of zest. Wash and chop chives into small pieces.
Heat a small saucepan over medium heat.
Add butter to saucepan and let it melt. Add flour and whisk until smooth.