KIFLIS (the best recipe: accept no non-yeasted non-sour-cream variants!)

My Irish Baptist grandmother learned how to make these Hungarian cookies from her in-laws, passed it to her daughters, and now I, the Korean adopted granddaughter, am the last person in the family who bakes them. I'm also pretty sure that they used to be our family's Rosh Hashanah cookies--but somebody converted, and that info's just lost to the aeons.

One day before baking, make components and refrigerate overnight, covered:
FILLING: combine 3 egg whites, 3/4 c. sugar, 2 1/2 c. ground walnuts.
DOUGH: combine 1/2 lb. soft butter, 3 c. flour, 3/4 c. sugar, 3 egg yolks, 8 oz sour cream, 1 envelope yeast dissolved in 1-2 oz warm water.
SHAPING: Dough handles best when cold. Use 1/4 dough at a time and keep the rest in fridge. Take this quarter of dough and notch into 12 portions (divide into fourths, then thirds). Pinch off one portion and roll into small ball on a very well-floured board or table. Using well-floured rolling pin, roll ball (with quick, light jabs) until about 1/4" thick or even slightly thinner, into a rounded triangle shape, flipping if if gets sticky. With a butter knife, smear the base of triangle with liberal smear of nut filling (about 1 1/4 tsp), not quite to the corners (so it won't leak). Then roll up, starting with the base, into a crescent, drawing the two points lightly toward each other. Place on ungreased cookie sheet (I use parchment). When you've got half of them shaped, turn oven to 375 degrees (or if this is your first time working the dough, 365 degrees), and bake 15 minutes. Start in fast on the second portion! Kiflis will be plump and lightly golden and ugly, well-browned on their bottoms, may crack a tiny bit over their swollen backs.
Now, at this point, we let them cool, then pop them into freezer bags and freeze until the day before we want them, or mail to cousins (they mail very well). Thaw on the counter, in the bag, the night before you want them. Frankly, they do NOT taste the same when they're fresh--the freezing seems to help the yeast and sour cream flavors meld. Then Christmas morning, roll them in powdered sugar (if you like--some of us prefer them without), and eat them with your milky coffee.
They are tender, extremely rich, and not quite like anything else I've tasted in the range of eastern European nut pastries.