Rinse beans in a colander under cold water. Snap or cut off the stem ends — line several up on a cutting board to trim multiple at once. Leave whole or snap in half. Add about 1 inch of water to a saucepan, set the steamer basket inside, and confirm the water sits below the basket holes. Have a snug lid ready.

Bring water to a boil over high heat, about 3 minutes. Add trimmed beans to the steamer basket in an even layer and cover tightly. Reduce to medium-high. Steam 4–7 minutes: 4–5 minutes for tender-crisp, 6–7 minutes for fully tender. Check at 4 minutes by piercing with a fork or tasting. Pull off heat at your preferred texture — beans keep softening from residual heat. Do not exceed 7 minutes or they turn mushy and dull. Beans are done when bright, vibrant green; a fork slides in with light resistance.

Remove steamer basket and discard water. Return beans to the warm pot off heat. Add a pat of butter and toss to coat — residual heat will melt it. Season with salt and black pepper. Finish with a squeeze of lemon if desired. Serve immediately. Don't let them sit; they'll keep softening and lose color.