2egg yolks and 1 teaspoon waterwhisked, for egg wash
In a medium bowl, whisk together sugar, salt and flour. Place flour mixture, cold butter and cream cheese in a food processor and pulse just until combined. You should have a crumbly dough. Then add in sour cream and vanilla. Pulse just until combined into a clumpy dough. Do not overmix.
(If you don't have a food processor, let butter and cream cheese come to room temperature. With a stand or hand mixer with beater attachment, cream together butter, cream cheese and sugar just until light and fluffy, about 1 minute. Then add in sour cream and vanilla and combine. Lastly, add in flour and mix just until combined. This method will lead to a chewier rugelach vs. the flakier cookie with cold ingredients but both are delicious.)
Lightly flour a clean surface and dump dough onto the surface. Divide the dough into four equal sized balls (I use a scale) and flatten each into a disk. Dough will be slightly sticky. Wrap each disk in saran wrap and chill for two hours or ideally overnight. It also freezes well for up to 2 months.
Pre heat oven to 350 F.
Roll out each ball into a 9 inch circle about 1/8 inch thick on a floured surface into a circle, keeping the other balls in the fridge until you are ready for them. Make sure to use enough flour to prevent sticking.
Eat a spoonful of Nutella.
Spread a thin layer of Nutella on the circle, sprinkle with sugar and hazelnuts.
Cut the circle into 12 triangles like a pizza. Roll up each triangle from the wide end, and secure the tip into the cookie so you have a little spiral. Place cookies on a parchment lined cookie sheet, and freeze for 30 minutes to prevent spreading. Repeat with other balls.
Brush rugelach with egg wash, sprinkle with more sugar and bake for 25 minutes or until golden. Cool for 5 minutes on the cooking sheet and then finish cooling on cooling rack.
Also, you will need to chill the dough for at least two hours.