Grandma C's Nut Roll

Directions

1. Add the walnuts and 1/2 c sugar to a food processor and pulse until the nuts are finely ground.
2. Whip the egg whites and remaining sugar into a meringue that holds stiff peaks and fold in the nut mixture. You don't have to be gentle here--the egg whites are just acting as glue, so you can fold without fear of deflating the whites. Set the filling aside.
3. Mix the yeast and warm water, set aside. In a stand mixer, cream the butter and sugar until the butter is light and fluffy. Add the yeast mixture. Beat the reserved egg yolks into the sour cream and add to the mixer bowl. Mix on low speed until combined, then switch to the dough hook and add enough flour to make a soft dough. Stop adding flour when the dough no longer sticks to the sides of the mixer bowl. Knead until silky smooth, 5-8 minutes. Divide the dough into three balls. Put in greased bowls, cover with plastic, and let rise in a warm place until doubled. When the dough is nearly risen, preheat the oven to 350° . Punch down one piece of dough and roll it into an oval about 14 long. The dough should be about 1/8 in thick. Spread 1/3 of the filling onto the dough, leaving 1 inch borders on 3 sides (both short sides and one of the long ones), and a border about 1/4 of the width of the oval on the remaining long side. Roll the nut roll long-ways, like a jelly roll, and set it, seam side down, on a greased sheet pan. Repeat with the remaining dough and filling.
4. Beat the egg together with a splash of water or milk to make an egg wash.
5. Brush the nut rolls with the egg wash and bake immediately, without waiting for them to rise.
6. They will take 25 - 30 minutes to bake, and are done when they're golden brown.
7. Cool the baked nut rolls on a rack. The cooled nut rolls freeze beautifully if well-wrapped in two or three layers of aluminum foil.