Preheat oven to 350 degrees F; spray baking sheet with cooking spray.
In a large bowl, combine the flour, cheeses, baking powder, salt, chili powder, and garlic powder (if using).
In another container, combine the milk, oil, and eggs, and whisk to combine well.
By hand (recommended) or with an electric mixer with paddle attachment (on low speed), gradually add the milk mixture to the dry ingredients, mixing until well blended and the dough is dry and crumbly (do not overmix!).
Turn the dough out onto a lightly-floured board and knead 8 times, then divide the dough in half.
Form each half into an 8-inch long roll and place them at least 6 inches apart on the sprayed baking sheet.
Carefully flatten each roll to a 1-inch thickness.
Bake at 350 degrees F for 30 minutes, then remove from oven; let the rolls cool on a wire rack.
Reduce the oven temperature to 325 degrees F.
Slice the rolls into 2/3-inch (approx) slices, diagonally; should make about 12 slices per roll.
Place the biscotti slices back on the baking sheet, cut side down, and bake at 325 degrees F for another 10 minutes; turn biscotti over and bake an additional 10 minutes."
Remove the biscotti from the sheet and allow to cool on a wire rack.