||Beat together butter and cream cheese until blended. Add flour all at once. Beat just until dough comes together. Divide dough into thirds. For rectangular rugelach, flatten each third into a 6″x 4″ rectangle. For crescent rugelach, flatten into a 6-inch circle. Wrap in plastic and refrigerate for an hour.
Preheat oven to 350°.
Whisk together sugar and cinnamon, and set aside.
Flour work surface and the top of one portion of dough.
For rectangular rugelach: Roll dough into 16″x 10″ rectangle 1/8-inch thick. Brush off excess flour. Spread 1/4 cup preserves on the dough, leaving a 1/4-inch border. Along the long edge of the preserves, place a line of chocolate chips or raisins. Sprinkle rem rest of the dough with about 2 teaspoons of the cinnamon-sugar mixture and about 2 & 1/2 tablespoons of ground nuts. Starting at the chocolate chip/raisin end, roll up the dough, gently tucking and tightening as you go. Turn the seam side facing down. Cut into 1 & 1/2-inch slices. Repeat with remaining dough.
For crescent rugelach: Roll each portion of dough into a 14-inch circle 1/8-inch thick. Spread 1/4 cup of preserves on each portion, leaving a 1/4-inch border. Sprinkle entire surface with 1/4 cup chocolate chips/raisins, cinnamon sugar, and 2 & 1/2 tablespoons nuts. Cut the circle like a pizza, making either 8 or 16 triangles. Roll up dough, starting from the wide end. Tuck the point underneath. Repeat with remaining dough.
Place on lined baking sheets. Sprinkle each cookie with about 1/8 teaspoon of cinnamon sugar. Bake about 25 minutes. The bottoms should be light golden and the tops blond. Cool on baking sheets on a rack until cookies firm slightly. Transfer to wire racks to cool completely.
Makes about 30 rectangular cookies, or 24 large crescent cookies, or 48 small crescent cookies.