Add 3 quarts of water and kosher salt to a large pot. Heat pot over high heat and bring to a rolling boil.: You will notice the water take on a lively movement quickly as it nears a rolling boil, with large bubbles breaking the surface, and the air will feel energized with steam, signaling that the pot is ready for the beans. This high energy boil is important because it shortens the cooking time for the green beans , helping them retain their bright color and snap. A common mistake is using too little water which drops the temperature when the beans are added, resulting in uneven cooking, so make sure the pot is large enough and the water is vigorously boiling before you add the vegetables.
In a medium-sized bowl combine 1 quart water and a handful of ice cubes. Set the ice bath aside.: The ice bath should look crisp and cold, with the cubes clinking and slowing as they cool the water. This chilly pool is essential to arrest the cooking process and preserve the emerald color of the green beans . If you skip this step, the residual heat will continue to soften the beans and they can quickly lose their ideal texture, so have the ice bath ready before you start boiling.
Add beans to the boiling water and cook until the green beans are bright green and crisp-tender, 4 to 6 minutes. Immediately transfer beans to the ice bath for 5 minutes. Drain well and pat dry with paper towels.: When the beans hit the boiling water you may hear a gentle sizzle and see the water briefly quiet as it absorbs the cooler temperature of the green beans . Watch for the instant color change to a vivid green, and check the texture by tasting a bean for a firm bite, not limp. Transferring immediately to the ice bath should cause a brief clouding of the bath as heat escapes, and after five minutes the beans will be glossy and completely cooled. A common pitfall is insufficient drying; water left on the beans will steam when they hit the butter , making the dish watery, so pat them thoroughly dry.
Heat a small sauté pan over medium heat, add the almonds and cook, stirring frequently, until lightly toasted. Transfer the almonds to a small bowl.: As the sliced almonds warm, they will emit a warm, nutty aroma and begin to show golden edges. The sound is subtle, a faint shifting as they move in the pan, and the visual cue is a light browning without smoke. Toasting brings out essential oils and deepens flavor, but watch them constantly because nuts can go from golden to burned in seconds. If they scorch, toss them and start again, because burnt nuts will add bitterness to the dish.
In a large sauté pan, melt the butter over medium-high heat. Add the green beans and garlic and cook, tossing to coat the beans, until the beans are warmed through and al dente, about 2 minutes. Season with salt and pepper and transfer to a platter. Top with the toasted almonds and serve.: The moment the butter melts it will release a rich scent, and when you add the smashed garlic you should notice its fragrance bloom and soften as it gently meets the hot fat. Tossing the green beans in this glossy mixture creates a sheen and warms them without overcooking, preserving their snap. Keep the heat at medium-high so the beans heat quickly, and listen for a gentle sizzle, which indicates the butter is doing its job. Overcrowding the pan or leaving the garlic in direct heat too long can lead to burning, so keep the beans moving and taste for final seasoning before plating.