Whisk flour, baking powder, xantham gum and salt together in medium bowl.
Using a stand mixer, beat sugar and butter on medium high speed until pale and fluffy, about 3 minutes.
Add eggs, water vanilla and almond extract and beat until well combined, about 2 minutes.
Reduce speed to low, add flour mixture and beat until completely incorporated and dough is homogenous, about 3 minutes, scraping down the bowl as needed.
Add almonds and beat until combined, about 30 seconds.
Cover bowl with plastic wrap and let dough rest for 30 minutes.
Adjust rack to middle position and heat oven to 350 degrees.
Line baking sheet with parchment paper.
Using a rubber spatula, transfer dough to prepared sheet.
Using wet hands, shape dough into 12 by 3.5 inch long rectangle.
Bake until golden and just beginning to crack on edges, about 35 minutes, rotating pan halfway through baking.
Remove biscotti loaf from oven and let cool for 10 minutes.
Reduce oven temperature to 325 degrees.
Transfer cooled loaf to cutting board and slice on bias into ½ inch thick slices using serrated knife.
Arrange slices, cut side down, on wire rack set in rimmed baking sheet, spaced ¼ inch apart.
Bake biscotti until crisp and lightly golden brown on both sides, about 35 minutes, flipping cookies halfway through baking.
Let cool completely before serving.