Heat oven to 350F. Line a baking sheet with parchment paper.
Sift together the flour, cocoa powder, baking powder, and salt. Set aside.
In a large bowl, cream together the butter and brown sugar. Add the eggs one at a time, mixing fully after each one. Then add the almond extract.
Stir the dry ingredients into the butter mix, until almost combined. Finish stirring it while adding the chopped chocolate.
Knead the dough into a cohesive mass in the bowl. Then dump onto a clean, lightly floured work surface. Shape it into a long flat log. It should be a little bit shorter than your prepared baking sheet, about 3 inches wide, and only about 3/4 inch tall.
Place the flat log onto your baking sheet, and bake for 30 minutes. Remove from the oven and allow to cool for about 15-20 minutes, until you can handle it more easily. Turn the oven down to 325F.
Using a sharp knife, slice the log on a diagonal into 1/2 inch slices. Separate the slices, lay them on their side, spread out onto the baking sheet.
Bake for another 5-6 minutes. Flip the slices over and bake for another 5-6 minutes. They should be more crisp and dry on both sides than when you sliced them. How dry you get them is up to you. If you want them more crisp, bake them for a couple minutes longer.
Allow to cool fully on a wire rack. While they cool, Melt about 1/2 cup of extra chocolate in the mircowave or over a pot of hot water. If you are familiar with tempering chocolate you can go ahead and temper it for drizzling. It's not 100% necessary though. I like to use a disposable piping bag to drizzle my biscotti, but you can also drizzle with a spoon. Simply drizzle as much chocolate as you like over your biscotti, and allow to cool and harden.