In a large bowl, beat together the first 6 ingredients at medium high speed with the whip attachment until thick and lighter colored (because of the espresso it will not get too light), about 5 minutes. Whisk together the flour and baking powder and then stir them into the wet ingredients. Fold in the chips. Cover tightly and chill for at least 3 hours–I find it best to do this much the day before to really firm up the dough, and I have let it chill up to 3 days.

Place the oven racks in the upper and lower middle levels. Preheat the oven to 350 F. Line 2 baking sheetswith silicone or parchment paper.

Separate the dough into 4 equal pieces, about 13 1/2 ounces each. Working with one piece at time (wetting your hands will help with sticking), shape the dough into logs, roughly 8 by 2 inches long, and place on the baking sheet. You will place 2 logs on each cookie sheet, about 2 inches apart.

Bake the logs for 28 minutes, rotating top to bottom and front to back halfway through. They should be lightly browned. Let them cool for at least 2 hours and up to overnight, before transferring them gently to a cutting board.

Turn the oven on to 300 F. Slice the logs into 1/2-1 inch slices, and then return them to their baking sheets, spacing them 1/2-inch apart and standing them upright (you want them to toast). Return them to the oven, and bake another 25 minutes, once again rotating front to back and top to bottom halfway through. They will become quite golden brown because of the espresso. Cool on the baking sheets–they will crisp up as they cool, but will never be really hard like a fat-free biscotti, but rather more crumbly, like a butter-based biscotti.