[xrr rating=4/5]
I used an Ikea Danish Cake Mix, and used this filling for half of the dough. It was a great hit.
1/3 cup sugar
1/8 cup unbleached all-purpose flour
1 1/2 tablespoons cold unsalted butter, cut into bits
1 tablespoons unsweetened cocoa powder
1/2 teaspoon ground cinnamon
1 egg white, beaten until foamy
1/4 cup mini chocolate chips
Make the chocolate streudel
1. In a medium bowl or a food processor, mix the sugar, flour, butter, cocoa, and cinnamon together. Cut the butter in with your fingers or process until crumbly.
Assemble the coffee cake
1. Punch down the dough and turn it out on a lightly floured board and knead lightly until smooth, 1 or 2 minutes. Cut the dough in half. Roll one half into a 10-by-14-inch rectangle. Spread evenly with half of the Chocolate Streusel. Roll up and place, seam side down, on a buttered baking sheet. Repeat with the remaining dough and filling, placing the loaf on a separate buttered baking sheet.
2. With clean scissors, snip each loaf at 3/4-inch intervals, cutting three-fourths of the way through the dough. Starting at one end, pull and twist each cut slice on its side to lie flat on alternate sides. Cover with a towel and let rise in a warm place until doubled in size, about 45 minutes.
3. Preheat the oven to 350°F (175°C). Brush the loaves with the egg white and sprinkle with the nuts. Place in the oven, reduce the heat to 325°F (160°C), and bake for 30 to 35 minutes, or until golden brown. Transfer the loaves to wire racks to cool completely. Cut into 3/4-inch-thick slices to serve. Or, wrap and freeze for up to 2 months.