Prep the beans: Rinse, dry, and trim the stem ends. Leave them whole for a nice look, or cut in half if you like bite-size pieces.
Choose your method: For the most consistent texture, blanch the beans in salted boiling water for 2–3 minutes until bright green, then drain and shock in ice water.
If you prefer one-pan cooking, skip blanching and proceed to the sauté with a splash of water.
Heat the pan: Set a large skillet over medium heat. Add the olive oil and half the butter. Let it melt and foam slightly.
Add the beans: If blanched, pat them very dry before adding to the pan.
If not blanched, add 2–3 tablespoons of water with the beans to help them steam. Toss to coat.
Season early: Sprinkle with salt and pepper. Cook, tossing occasionally, until the beans are crisp-tender and lightly blistered in spots, about 3–5 minutes if blanched, 6–8 minutes if raw (add another splash of water if the pan gets dry).
Add the garlic: Push the beans to one side.
Add the remaining butter to the open space, then the minced garlic. Let it sizzle gently for 20–30 seconds until fragrant, not brown.
Combine and finish: Toss the beans with the garlicky butter. Add lemon zest, a squeeze of lemon juice, and red pepper flakes if using.
Taste and adjust salt and pepper.
Serve hot: Transfer to a warm platter. Top with toasted almonds, Parmesan, or parsley if you want an extra flourish.