Step 1Heat the oven to 325 degrees. In the bowl of a stand mixer or in a large bowl using a hand mixer, cream together the butter and sugar. Beat in the eggs, one at a time, then add the almond extract.
Step 2In a medium bowl, whisk together the flour, baking powder and salt. With the mixer running, slowly incorporate the dry ingredients into the butter mixture. Add the sliced almonds and mix for a minute more. You will have a soft dough.
Step 3Put the dough on a floured board and divide it into thirds. Roll into logs about 1 1/2 inches in diameter. Place the logs on a parchment-lined baking sheet, spaced about 3 inches apart, and bake for 25 to 30 minutes, or until slightly browned. Remove the logs and let them cool slightly.
Step 4While the logs are still warm, cut them on the diagonal into slices about one-half-inch thick. Place the slices on two baking sheets and bake for 5 to 10 minutes, or until barely brown. Turn over the biscotti and bake an additional 5 to 10 minutes, until barely brown. Cool on a rack.