HEAT OVEN to 325F (163C). Line a large baking sheet with parchment paper.
MIX WET INGREDIENTS: In a large bowl, mix egg and sugar with a fork until well combined. Add vanilla and oil. Mix until smooth.
1 large egg, 1/2 cup sugar, 1/2 cup vegetable oil, 1/2 teaspoon vanilla extract
STIR IN DRY INGREDIENTS: First stir in baking powder and salt into sugar egg mixture to combine evenly. If choosing an orange flavor, stir in 1 teaspoon finely grated orange zest. Then add flour and mix with spatula until well combined. Then stir in rice krispies, chocolate chips and nuts.
1 cup all purpose flour, 1 teaspoon baking powder, 1/4 teaspoon kosher salt, 1 cup rice krispies cereal, 1/2 cup chocolate chips, 1/2 cup unsalted nuts, roughly chopped, Note 1
SHAPE DOUGH: Scoop out dough onto a lightly floured surface. Divide dough into 2 pieces. Dough will be sticky. Wet your hands and shape each piece of dough into a 9 inches (23 cm) long log. Pat to flatten top of logs a little. Place logs on parchment lined baking sheet, leaving enough room between logs as biscotti will spread. Brush on egg wash for a golden finish - this is optional.
FIRST BAKE: Bake biscotti logs in center of oven for 30 minutes. Remove and let cool 10 minutes. Transfer to cutting board. Slice logs horizontally into 3/4 inch (2 cm) pieces using a serrated knife (bread knife). You will have a total of 20-22 pieces. Lay pieces back on baking sheet, cut side up Sprinkle tops with cinnamon sugar if using.
SECOND BAKING: Bake again in preheated oven for 15 minutes until golden brown and dry. Let cool completely, then store in an airtight container.