In a stand mixer, beat together the Butter (3 stick) and Cream Cheese (12 ounce) with the paddle attachment.
Add the Salt (1/2 teaspoon) and Granulated Sugar (1/4 cup) and beat until light and fluffy at medium low to medium.
Reduce speed to low and add the Unbleached All-Purpose Flour (3 cup) in 1/2 cup increments until just combined.
Turn the dough out onto a lightly floured surface and work it into a ball. Divide the dough into 4 equal pieces and and press each into a rough rectangle shape.
Wrap in plastic wrap and refrigerate at least 2 hours and up to 2 days.
Put the Granulated Sugar (1 cup), Brown Sugar (1/2 cup), Ground Cinnamon (2 1/2 tablespoon) and Walnut (2 1/2 cup) into the work bowl of a food processor.
Pulse together until the nuts are finely chopped, but still have some texture. Set aside.
In the bowl of a mini prep food processor, pulse the Apricot Preserves (1 cup) until smooth and transfer to a bowl. Rinse the food processor and process the Strawberry Preserves (1 cup) until smooth. Transfer to another bowl and set aside.
Generously flour your work surface. Working with one piece of chilled dough at a time, place the dough on the floured surface. Roll the dough into a rectangle about 12 x 5 inches. Use a pizza cutter to even up the sides and edges.
Spread about a half cup of jam evenly over the surface of the dough. Sprinkle a third to a half cup of the cinnamon, nut mixture over the top of the jam and lightly press it in with your fingertips.
Starting on the long end, roll the dough, jelly-roll like into a cylinder. Wrap the cylinder in plastic wrap, place on a baking sheet and refrigerate. Continue with the remaining rectangles of dough.
Refrigerate the logs of dough at least 4 hours or preferably overnight. Reserve the remainder of the cinnamon sugar mixture for rolling the cookies in.
Arrange the oven racks to the top and bottom thirds of the oven. Preheat the oven to 375 degrees F (190 degrees C). Prepare two large baking sheets with 2 pieces of parchment each. Set aside.
In a small bowl, whisk together the Egg (1) and Milk (1 tablespoon) for an egg wash. Set aside. Add the cinnamon nut mixture to another small bowl and set aside.
Working with one roll of dough at a time, brush the dough on all sides with the egg wash.
Use a serrated knife to cut the roll into 1" slices. Toss each slice in the cinnamon sugar mixture, lightly pressing the coating and nuts into the cookie.
Arrange the cookies a few inches apart on the parchment paper.
Place one cookie sheet on the top shelf and the other on the bottom shelf. Bake for approximately 10 to 12 minutes, then swap their positions in the oven, moving the top pan to the bottom and vice versa and turning them 180 degrees.
Bake for an additional 10 to 12 minutes until the rugelach are brown.
Remove from the oven and cool a few minutes on the cookie sheet before using a thin spatula to transfer the cookies to a cooling rack. When the cookies reach room temperature, they can be stored in an airtight container for up to a week and can be frozen for up to a month.