PREHEAT oven to 350° F.
BEAT butter and sugar in large mixer bowl until light and fluffy. Beat in Nestea, egg yolk and vanilla extract. Gradually stir in flour. Drop by heaping teaspoon 2 inches apart onto ungreased baking sheets.
BAKE for 12 to 15 minutes or until lightly golden around edges and centers are set. Cool on baking sheets for 2 to 4 minutes; remove to wire racks. Brush with glaze; cool completely.
COMBINE 1 cup sifted powdered sugar, 5 teaspoons hot water and 1/4 teaspoon vanilla extract in small bowl; stir until smooth.