Heat butter in a skillet over medium-low heat; cook and stir sesame seeds until lightly toasted, 3 to 5 minutes. Add lemon juice, parsley, salt, and pepper; stir until evenly combined.

Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add asparagus, cover, and steam until tender, 2 to 4 minutes.

Transfer asparagus to a serving plate and drizzle sesame-butter over the top.