Melt 1 tablespoon butter in a heavy saucepan over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add whipping cream; cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Stir in salt and pepper. Add drained Brussels sprouts, and toss gently. Place in a serving dish, and keep warm.
Sauté pecans in remaining 2 tablespoons butter in a small skillet about 5 minutes. Drain pecans, and sprinkle over Brussels sprouts.