Preheat your oven to 350 and line a baking sheet with parchment paper.
Cream butter and sugar together until light and fluffy - about a minute or so.
Add in eggs, one at a time, until well incorporated.
Mix in vanilla.
In a separate mixing bowl, add your flour, cocoa powder, baking soda, and salt together. Gradually add this into the mixer with the wet ingredients.
Add in chocolate chips. I like to fold ours in with a spatula, but you can also just throw them right into the mix in mixer.
Lightly flour a working surface for your dough. Then scrape the dough together in the mixing bowl with a spatula and move it to your floured surface.
Lightly dust your dough with flour and also be sure to flour your hands lightly so that the dough doesn't stick. Work the dough into a ball, adding a bit more flour if you need to in order for it to be workable and not sticky.
Divide the ball into two equal size pieces.
Move each piece onto your parchment paper covered baking sheet and form each into "logs" that are about 2" wide and 3/4" thick. Be sure to give them space apart on the sheet because they will expand while baking.
Once you have your "logs" formed, bake at 350 for 35 minutes.
Once cooked, be sure they are firm to the touch before cutting. I typically cut them immediately, but you can wait a few minutes if you prefer. Just don't let the biscotti cool too much or it will be more difficult to cut. Cut on the diagonal to form the biscotti. (You can remove from the baking sheet if you like, but I just do mine right on that surface.)
Turn the cut biscotti on their sides on the baking sheet. Return to the 350 oven for 10 minutes for the second bake.
Let the biscotti cool about 2 minutes on the baking sheet and then move to wire racks to finish the cooling process.
Store in a sealed container.