Preheat oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats. Set aside.

Whisk the flour, sugar, baking powder, and salt together in a large bowl until combined. Using a pastry cutter or fork, cut in the butter until the mixture is crumbly. Set aside. In a medium bowl, whisk the 3 eggs, oil, and vanilla extract together. Pour into the flour/butter mixture and gently mix together with a wooden spoon or silicone spatula until everything is just barely moistened. It will be very crumbly, see photo above for a visual.

Turn dough out onto a lightly floured surface and with floured hands, knead lightly until the dough is soft and slightly sticky, about 8-10 times. If it’s sticking all over your hands, knead 1-2 more Tablespoon(s) of flour into the dough. Divide the dough in two and place each half onto a baking sheet. Shape each half into an 8-9 inch long slab, patting down until each is about 1/2 inch thick. Using a pastry brush, lightly brush the top and sides of each biscotti slab with egg wash.

Bake in batches (or together) for 25-26 minutes, or until the top and sides of the biscotti slabs are lightly browned. Remove from the oven, but do not turn off the heat. Allow to cool for 10 minutes. Once the slabs are cool enough to handle, cut each into 1 inch wide slices. Set slices cut sides upright, 1/4 inch apart, on the baking sheets. (It’s tricky to set the end slices upright, so just turn them over.) Return to the oven to continue baking for 8 minutes. Turn biscotti over and bake other side for 8 minutes. The cookies will be slightly soft in the centers with harder edges.

Remove from the oven and cool the biscotti for 5 minutes on the baking sheet. Transfer to a wire rack to cool completely before dipping in white chocolate. The biscotti becomes more and more crunchy as it cools. It’s helpful to save the baking sheets for the next step.

Melt the chopped white chocolate in a double boiler or carefully use the microwave. For the microwave, place the white chocolate in a medium heat-proof bowl. Melt in 15 second increments, stirring after each increment until completely melted and smooth. Dip each cookie in the melted chocolate and place back onto the baking sheets. Allow chocolate to set in the refrigerator or at room temperature.

Biscotti stays fresh covered at room temperature or in the refrigerator for 1-2 weeks.