Cream the butter.
Gradually add the sugar, creaming well.
Add the egg yolk and vanilla; beat well.
Sift together the flour, baking powder, and salt.
Add to the creamed mixture and knead with your hands to make a smooth dough.
Divide the dough into two parts.
Place on waxed paper and shape into long rolls 1 1/4 inches in diameter, about 8 inches long.
Wrap in the waxed paper and chill at least 1 hour, or until the dough is firm enough to slice.
Just before baking, beat the egg white slightly and brush the chilled cookie rolls.
Combine the almonds and remaining 2 tablespoons sugar.
Roll the coated dough in the mixture, pressing the nuts in firmly.
Slice about 1/4 inch thick and place on a lightly greased cookie sheet, spacing the cookies about 1 inch apart.
Bake in a 350° oven for about 8 minutes, or until faintly browned around the edges.