Baby Brussels Sprouts with Buttered Pecans

Put oven rack in middle position and preheat oven to 350°F.
Spread pecan pieces in 1 layer in a shallow baking pan and bake until fragrant and a few shades darker, about 10 minutes. Add 1/2 tablespoon butter and 1/4 teaspoon salt to nuts and toss until butter is melted and nuts are coated.
While nuts bake, cook Brussels sprouts in a 6- to 8-quart pot of boiling salted water, uncovered, until just tender, 5 to 6 minutes, then transfer to a bowl of ice and cold water to stop cooking. Drain sprouts and pat dry.
Melt remaining 2 1/2 tablespoons butter in a 12-inch heavy skillet over moderate heat, then add garlic and cook, stirring, until fragrant, about 1 minute. Increase heat to moderately high, then add sprouts and sauté, stirring occasionally, until browned in patches, about 5 minutes. Add lemon juice, pepper, and remaining 1/2 teaspoon salt, then stir in pecans and serve.