Preheat oven to 325 degrees F
In the bowl of a stand mixer (or with a hand mixer), beat together butter, sugar, salt, vanilla extract and baking powder on medium high speed until pale and smooth, about 3-4 minutes.
Add the eggs, scrape down the sides of the bowl, and continue beating on medium-high speed until combined, another 3-4 minutes.
Add flour, espresso powder and cocoa powder and mix on low speed until just combined. Add almonds and mix for another 30 seconds, or stir in until evenly distributed.
Using a bowl scraper or silicone spatula, transfer the dough to a large baking sheet lined with parchment or a silicone baking mat. To make 12 large biscotti, shape dough into one log, about 9 x 4 inches (it should be about 3/4 inch thick). To make 24 smaller biscotti, shape into two logs, about 9 x 2 inches. Set the logs at least 2 inches apart because they will spread while baking. I find it helpful to dampen my hands when shaping the dough, since it is very sticky.
Bake biscotti in preheated oven for 25 minutes. Remove from the oven and let cool for five minutes. Spritz log(s) generously with water and let sit again for 5 minutes. This helps to soften the cookie just enough to make slicing much easier.
Remove the log(s) to a cutting board and slice on the bias with a sharp knife or a serrated bread knife. A straight down motion, or a sawing motion with the serrrated knife works well. Place the cookies back on the baking sheet with space between them, and bake for another 20-25 minutes (smaller cookies will need a little less time), until they feel quite dry.
Cool biscotti completely on the baking sheet and dip or drizzle with melted or tempered chocolate once cooled.