Preheat the oven to 325 and line a large baking sheet with parchment paper.
In a large bowl, whisk together eggs, oil, vanilla extract, and espresso until smooth.
Whisk in both sugars.
Add flour and baking powder and start whisking until it becomes too thick. You can either use a rubber spatula or your hands to finish mixing the ingredients. The dough will be thick but still sticky.
Grease your hands with a little bit of oil so the dough doesn't stick to your hands and it's easier to handle.
Separate the dough, place them on the prepared baking sheet in two and form each piece into a roll that's a little less than an inch thick and about 4 inches wide. Leave a little space between the logs.
Bake for about 30 minutes. Take out of the oven and immediately cut the loaves into about 1/2 inch thick slices with a serrated knife.
Place the slices on its sides and bake for another 15-20 minutes. (You can bake a few minutes less or more depending on how crispy you like your biscotti.)
Let biscotti cool completely before dipping in chocolate.
Melt dark chocolate wafers in the microwave or in a double boiler.
Dip each biscotti bottom in chocolate and place the biscotti back on the baking sheet upside-down (chocolate covered bottom will be up) so that it solidifies evenly. Placing it upside down is not necessary but it looks nice.
(*Keep biscotti in an airtight container, like a cookie jar at room temperature.)