Melt butter around the sides and bottom of a heavy saucepan. Add milk and sugar. Stir with wooden spoon toward the center of the pan. Add marshmallows.
Place 1/4 cup sugar in small pan to caramelize (a cast iron pan works well but is not required). Turn pan frequently to prevent burning.
Transfer melted sugar into the larger pan, stirring constantly. Lower the heat, and cook until a candy thermometer reaches 238°F, stirring often; set aside to cool to 110°F.
Stir in vanilla and pecans, continuing to stir until the candy will hold its shape. Drop by teaspoonfuls onto buttered wax paper, parchment paper or silicone sheets.
Makes approximately 30 pieces.
