Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a mixing bowl, whisk together the flour, baking powder, and salt.

In another bowl, beat the sugar and eggs until light and fluffy. Stir in the orange zest and vanilla extract.

Gradually add the dry ingredients to the wet mixture until combined. Fold in the chopped almonds if using.

Divide the dough in half and shape each half into a log about 12 inches long and 2 inches wide on the prepared baking sheet.

Bake for 25-30 minutes, or until the logs are golden and firm to the touch.

Remove from the oven and let cool for 10 minutes. Slice the logs diagonally into 1/2-inch thick pieces.

Place the biscotti cut side down on the baking sheet and bake for an additional 10-15 minutes until crisp.

Let the biscotti cool completely on a wire rack before serving.