Prepare the dough by processing sugar, butter, egg yolks, and sour cream/cream in a food processor until well combined.

Add flour and yeast to the mixture and process again until a dough forms.

Refrigerate the dough overnight.

The next day, remove the dough from the refrigerator about 1.5 hours before baking to let it thaw.

Prepare the walnut filling by making a syrup from boiling water and sugar.

Stir in the crushed walnuts.

Remove the mixture from heat and stir in the sultanas.

Allow the filling to cool completely.

Divide the dough into three equal parts.

Roll out each part to approximately 0.5 cm thick.

Spread the cooled walnut filling evenly over each rolled-out dough portion.

Roll each filled dough portion up tightly, resembling a Swiss roll.

Place the rolled beigli in a baking dish.

Brush the surface with beaten egg yolk.

Place the baking dish in a warm place for 1 hour to allow the beigli to rise.

Brush the risen beigli with beaten egg white.

Place the beigli in the refrigerator for another 30 minutes to enhance shine during baking.

Bake in a preheated oven at 200 degrees Celsius (moderately hot) for 35-40 minutes, or until golden brown.