Dissolve yeast and 1 teaspoon sugar in warm water. Set aside.

In a medium sized mixing bowl, combine the flour and salt. Cut in cold butter until it resembles pea-sized chunks, as you would for making pastry.

Add the egg yolks and yeast mixture, and knead until it feels smooth and looks a bit shiny. Divide dough into 2 portions, cover, and set aside.

In a separate bowl, beat egg whites until soft peaks form. Gradually add the sugar, and continue beating until the mixture is stiff. Fold in vanilla.

On a lightly floured work surface, roll 1 portion of dough into a 9x13-inch rectangle. Spread with half of egg white mixture and sprinkle with half of the nuts. Roll up jelly roll style; repeat with remaining portion of dough.

Place each roll, seam side down, on a greased cookie sheet, and using a very sharp knife, slash along entire length of roll (don't quite cut through the entire first layer).

Bake at 375 degrees for 20 minutes or until brown. Cool on wire racks, and cut into slices.