Preheat your oven to 350°F (175°C).

In a large bowl, mix together the flour, cocoa powder, baking powder, and salt until well combined.

In another bowl, whisk together the melted butter and sugar until smooth.

Add the eggs and vanilla extract, mixing until fully incorporated.

Gradually add the dry ingredients to the wet ingredients, stirring until combined.

If using chocolate chips, fold them in gently at this stage.

Divide the dough into two equal parts and shape each part into a log on a baking sheet lined with parchment paper.

Bake in the preheated oven for about 25 minutes or until the logs feel set and a bit firm to the touch.

Let them cool for a few minutes, then slice the logs diagonally into biscotti pieces using a sharp knife.

Place the sliced biscotti cut-side down on the baking sheet and bake for an additional 10-15 minutes until they are crispy.

Allow the biscotti to cool completely before serving.