Wash asparagus and line them up on a cutting board with the tops even. Cut off tough bottom ends.
Bring a skillet or oval casserole filled half full with salted water to boil. Dump in asparagus all at once. When water returns to the boil, cook asparagus until crisp-tender, about 1 to 3 minutes, depending on size. Drain.
Return asparagus to hot pan, squeeze lemon juice over top. Add butter and a drizzle of olive oil, tossing to coat. Add kosher salt, to taste. Serve immediately.