Combine first 4 ingredients in a Dutch oven; cook over medium heat, stirring constantly, until sugar dissolves. Add 2 tablespoons butter; stir until butter melts. Cover and boil mixture 3 minutes.

Remove cover, and continue to cook, without stirring, until mixture reaches soft ball stage (234°). Remove from heat, and without stirring, add remain¬ing butter, pecans, peanut butter, and vanilla. Cool 10 minutes.

Beat mixture until well blended, and pour immediately into a buttered 9-inch square pan. Cool and cut fudge into 1 1/2-inch squares.