Dough:

1. Whisk together the flour, yeast, and salt. Mix in the butter and blend with your fingers until crumbly.
2. Add egg, oil, lemon juice, and kefir milk (or sour cream), and mix until incorporated.
3. Knead the dough on a floured surface for 5 minutes, or until no longer sticky. Add more flour if necessary.
4. Form into a ball, and to follow tradition, mark with a +, symbolizing a cross.
5. Cover with plastic wrap and refrigerate 5 hours, or overnight. Or freeze up to several weeks.

Filling:

1. Mix flour, sugar, walnuts, and cardamom. Add vanilla to melted butter and pour slowly into flour mixture while stirring. Stir until the mixture is smooth. (You should end up with a beautiful streusel consistency, once cooled.)

Assembly:

1. Preheat oven to 350°F.
2. Melt the 3 extra tablespoons of butter and set aside. Remove dough from refrigerator and divide into 8 equal portions. (I did this and the filling by weight.)
3. Roll each dough ball into a 10 x 6” rectangle. Brush with melted butter. (I found that the filling adhered to the dough just fine without the added butter and since there is a full pound in the recipe, decided it was fine to leave this step out.)
4. Spread 1/8th of the filling over each rectangle, leaving a ½-inch border. Cover with a piece of parchment paper. Press down lightly with your hands, so that the filling adheres to the dough. Fold the edges in ½-inch over the filling.
5. Roll into a cylinder. Gently flatten with the palms of your hands. (Do this because they puff quite a lot in the oven.)
6. Cut each roll into 6 pieces and arrange on 2 parchment lined cookie sheets. Brush liberally with the egg glaze.
7. Bake for 25-35 minutes, or until golden brown.