To make the dough in a food processor: Place 2 cups flour and ½ tsp Kosher salt in work bowl fitted with standard blade. Pulse to combine. Add ½ lb cream cheese, chopped into large chunks, and run machine until it's fully dispersed into the flour. Add ½ lb butter in large chunks and run machine until dough starts to clump. Dump out onto a large piece of plastic wrap and form into a flattish disc.
To make the dough with a stand mixer: Let ½ lb butter and ½ lb cream cheese soften at room temperature. Beat both together until light and fluffy. Beat in ½ tsp salt. Add 2 cups flour, beating until it disappears. Scrape dough onto a large piece of plastic wrap and form into a flattish disc.
Both methods: Chill dough until totally firm, about 2 hours in the fridge or about 30 minutes in the freezer. (Dough keeps in the fridge for up to a week, and in freezer much longer.)
When ready to bake: Heat oven to 350°F (175°C). Line a couple baking sheets with parchment paper.
Make the cinnamon sugar. Stir 1½ Tbsp cinnamon and ⅔ cup sugar together in a small dish. Place 1 cup chocolate in a second dish.
Roll out the dough and assemble. Divide dough into quarters and roll first quarter out on a floured counter into a rectangle about 12" wide and 7-8" long, with the widest side to you. Thinly spread 2-3 Tbsp of jam on dough, covering all but the furthest ¼ inch from you. The cookies seal better if you leave the top area bare. Sprinkle with 2 Tbsp cinnamon-sugar mixture, then 4 tsp chocolate.
Roll the cookies. Roll dough from the 12-inch side in front of you into as tight a log as you can, using your fingers to lightly seal the ends onto the log. Repeat with remaining logs.
Shape the cookies. Place log of filled dough in freezer for 10 to 15 minutes; it will cut more easily if semi-firm. Trim ends off each log so they have a clean shape. Cut log into 10 to 12 even slices. Arrange rugelach on prepared baking sheets a couple inches apart from each other.
Bake the rugelach. Brush tops lightly with egg wash and sprinkle with a total of 1 tsp of the remaining cinnamon-sugar mixture. Bake for 20-25 minutes, or until golden brown on top. Cool only a few minutes on baking sheet before transferring to a cooling rack.
Storage: Cooled cookies keep in a container at room temperature for a week, and in the freezer for a month.