In a large bowl, beat the butter, cream cheese, sugar and salt until smooth and creamy; add the flour and beat on low speed until you have a soft dough.
Divide the dough into quarters and let rest for 10 minutes, or wrap and refrigerate for an hour, or overnight. When you’re ready to bake, preheat the oven to 350?F.
On a lightly floured surface, roll each piece out into a 10-inch circle. Spread with a spoonful of tahini (about 2 Tbsp). In a small bowl, stir together the sugar and cinnamon, and sprinkle about 1 Tbsp overtop. Sprinkle with dark chocolate.
Cut the circle into quarters, and then each quarter into three, making 12 wedges. Roll each one up like a croissant, and place on a parchment-lined baking sheet. Make for 15-20 minutes, or until golden. Makes 4 dozen rugelach.