Preheat oven to 350 degrees with racks being placed evenly in the middle. Line two baking sheets with parchment paper.
Whisk together flour, baking powder and salt in a medium mixing bowl. In a separate bowl, with an electric mixer, beat together eggs until light and yellow. This should take about 2 minutes. Add in your sugar and mix well. Add in melted butter, beat again. Finally add in your vanilla and mix until incorporated.
Add dry ingredients to wet, in 2 to 3 increments. Don't overmix, mix until just incorporated. Add in kit Kat, or desired chocolate and mix together with your hands or a wooden spoon. I like to save a few pieces of kitkat to add to the biscotti right before cooking!
Divide your dough evenly into two. Form your dough into a long log like shape, roughly 3/4 of an inch high. The more uniform the better. This will give you similar shaped cookies throughout. Bake for 25 to 30 minutes or until edges start to brown. Cool for 10-15 minutes.
Place logs onto a cutting board and using a serrated knife, cut at an angle, into 1/2 inch cookies. Place cookies cut side up back on baking sheet. Bake 8 minutes, remove from oven, flip to other side and bake for additional 8. Remove from oven and cool.
For an extra rich taste, once cooled, dip the ends into melted chocolate.