egg wash:1 large egg beaten with 1 teaspoon milk or cream
Preheat oven to 350ºF (177ºC). Line a large baking sheet with parchment paper or a silicone baking mat. Lightly flour the baking sheet. Set aside.
In a medium size bowl, whisk together butter, oil, egg, vanilla, and sugar until combined. Set aside.
In a large bowl, toss together the flour, baking powder, salt, and mini chocolate chips.
Add the wet ingredients to the dry ingredients and gently mix with a large wooden spoon or sturdy rubber spatula until everything starts to come together. Mixture will be crumbly. This is ok. It will come together in the next step.
Check out this Instagram reel to see how I make my biscotti. Turn dough out onto lightly floured baking sheet and, with floured hands, pat dough into a rectangle about 1/2" thick. My rectangle was 6" wide and 7 and 1/2" long (using a ruler or a ruled silicone baking mat is helpful here). Brush the slab with the egg wash and sprinkle with coarse sugar.
Bake dough slab for 20-22 minutes, or until the top and sides of the slab are lightly browned. Remove from the oven, but do not turn off the heat. Place baking sheet on a wire rack and allow to cool for 10 minutes.
Once the dough is cool enough to touch, cut into 1" thick slices using a sharp knife. Cut these 1" slices in half, making a perpendicular slice down the entire slab. Set slices cut sides up on the baking sheet. Return to the oven to bake for 6 minutes (8 minutes if you want them extra crunchy). Remove from oven, turn biscotti over, and bake the other side for 6 minutes (again, 8 minutes if you want them extra crunchy).
Remove from the oven and allow to cool for 3 minutes on the baking sheet (cookies will become crunchier as they cool). Transfer biscotti to a wire rack to cool completely. Store biscotti in an airtight container for up to 1 week. Baked biscotti may be frozen up to 3 months. Thaw at room temperature.