In the top of a double boiler,melt the butterscotch chips over hot water until smooth. Stir in sweetened condensed milk and vanilla. Stir in chopped pecans,mixing well and chill until firm enough to handle. Form into a 10-inch-long roll on wax paper. Roll tightly in the wax paper to shape evenly.
Unwrap and mark the surface lengthwise with the tines of a fork, and brush with the egg white. Press the pecan halves into the roll to completely cover the surface. Rewrap in wax paper. Chill 2 hours or overnight. Cut into 1/2-inch slices with a sharp knife.