I used this recipe from Joy the Baker for Peanut Butter Pecan Biscotti, but I of course made a few changes. Mostly no pecans, add chocolate.
4 tablespoons butter, softened (this should be unsalted, but I used salted and it was fine)
1/3 cup natural peanut butter
1 cup granulated sugar
1 large egg
1 large egg yolk
2 cups flour
1 teaspoon baking powder
1/4 teaspoon salt
Place a rack in the center and upper third of the oven and preheat to 325 degrees F. Line two baking sheets with parchment paper and set aside.
In a medium bowl, whisk together flour, baking powder and salt. Set aside.
In the bowl of an electric stand mixer fit with a paddle attachment, beat together butter, peanut butter and sugar. Scrape down the bowl and add egg and egg yolk. Beat on medium speed until well blended then add the dry ingredients.
Divide the batter between the two baking sheets and shape dough into two oval/square log things.
Bake 30 minutes (she suggests switching racks halfway through, which I did). Remove from the oven and allow to cool on the baking pans until cool enough to handle, but still soft. Use a serrated knife to slice biscotti about 1-inch thick. Return to the baking sheet and bake for another 10 to 15 minutes….then I dipped the cooled cookies in melted dark chocolate.