Mix butter, milk and sugar in heavy 5-quart saucepan. Bring to full boil on medium heat, stirring constantly. Continue boiling exactly 10 minutes on medium heat or until candy reaches 234° (soft ball stage), stirring constantly to avoid scorching. Remove from heat. Gradually stir in marshmallow cream, peanut butter and vanilla, stirring until creamy. Add pecans and mix well. Pour into jellyroll pan (approximately 12 x 15 x 1-inch) that has been lightly buttered. Cool at room temperature. Cut into squares when cool. Makes 6 lbs.