Combine butter, add sugar gradually; beat in egg yolks and vanilla. Blend in flour and salt; chill. Shape level teaspoonfuls of dough into rounds; dip in egg white, then roll in the pecans. Put on greased cookie sheets. Bake at 375 degrees for 5 minutes. Remove from oven; make a depression in center of each cookie. Return to oven; bake about 10 minutes longer. Cool and fill centers with tinted butter frosting. Makes 6 dozen. To make tinted frosting, combine butter, sugar, cream and vanilla. Mix well. Divide mixture in half. Color one portion with red food coloring; the other with green food coloring. ----