Preheat oven to 350 F with rack in center. Line a baking sheet with parchment paper or aluminum foil. Set aside.
Sift the flour, baking powder and salt into a medium bowl. Set aside. Place the eggs and sugar in a large mixing bowl and beat on high until fluffy and light, about 2 minutes. Add the vegetable oil and almond extract, and beat until the oil is incorporated and the mixture is thick and smooth, about 1 minute. Reduce mixer to low and beat in the flour mixture. The dough will be quite thick. Knead in the nuts.
Turn the dough out onto a lightly floured surface. Flour your fingers and divide the dough in half. Transfer one portion of the dough to one long side of the prepared baking sheet and mold it into a smooth log 14 inches long, 2 1/2 inches wide and 3/4 inch high. Repeat the process with the second piece of dough, and place it 2 inches away from the first log.
Bake for 30 minutes until light brown and slightly puffed. Remove pan from oven, but do not turn it off.
Using a serrated knife, carefully cut the logs in 3/4-inch slices on a slight diagonal. Take care not to tear the parchment or silicone pan liner. Arrange the slices, standing upright, on the baking sheet leaving 1 inch between cookies. Return to the oven and bake 10 minutes longer, until the cut surfaces of the cookie have browned slightly and the biscotti are dry to the touch. Transfer to wire rack and cool completely.
Melt 8 ounces of bittersweet chocolate with 6 tablespoons unsalted butter in the microwave. Scrape the chocolate onto a shallow plate and dip one long flat side of each cookie in the chocolate so it comes halfway up the sides. Place each dipped cookie on a wire rack, uncoated side down. Let the chocolate set.