Heat the oven to 350°F. Line a baking sheet with parchment or a silicone mat. Make sure the butter is soft. (Or microwave it on a low setting for a several seconds to take the chill off.) Get a wire rack handy.
Combine the flour, baking powder, and salt in a medium bowl; stir with a fork to break up any clumps. In a large bowl, use an electric mixer to cream together the butter and the sugar until light and fluffy; add the eggs, one at a time, and beat until light and fluffy, then add the vanilla. Add the dry ingredients to the egg-butter mixture a little at a time, beating until just combined.
Divide the dough in half and transfer them to the center of the prepared baking sheet. Roll and pat each half into a loaf about 2 inches wide; dust your hands lightly with almond flour if necessary to keep them from sticking. Bake for 35 to 40 minutes, until they’re golden and beginning to crack on top. Cool the logs on the sheets for a few minutes to set, then transfer to the rack with a spatula. Lower the oven temperature to 250°F.
When the loaves are cool enough to handle, carefully transfer them to a cutting board and use a serrated knife to slice each on the diagonal into 1/2-inch-thick slices. Put the cookies on the paper again, sliced side up; it’s okay if they’re close to each other. Return the pan to the oven, and bake until the biscotti are dry, 90 minutes to 2 hours, depending on how firm and dark you like them. Turn once or twice during baking so they color evenly. Transfer them to the rack to cool.
If you want them dipped, put the chocolate in a small bowl (or pot) and melt in the microwave (or on the stove) over low heat, stirring occasionally. Put the chopped almonds on a plate. Dip each biscotti in the melted chocolate and immediately roll in nuts. Return to the rack for the coating to harden. The biscotti will keep in an airtight container for several days. (Or the freezer for a couple months.)
— Recipe developed by The Bittman Project for Bob’s Red Mill