Preheat oven to 350°F. Line a baking sheet with parchment paper. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar together until light and fluffy, about 2 minutes.
4 tablespoons unsalted butter, ½ cup granulated sugar
Add the eggs, vanilla extract, and almond extract, if using. Mix on low speed, just until combined.
2 large eggs, 1 teaspoon pure vanilla extract, ¼ teaspoon almond extract
In a small bowl, combine the flour, almond flour, and baking powder.
1¼ cups all-purpose flour, ¼ cup almond flour, 1 teaspoon baking powder
With the mixer on low speed, slowly add the dry ingredients into the wet ingredients. When all of the dry ingredients have been incorporated, gently fold in the sliced almonds. Make sure not to over mix the dough!
½ cup sliced almonds
Shape the dough into a 6x14-inch log.
Bake the biscotti log for 25-28 minutes, or until it is set in the center and beginning to brown on the edges.
Slice the biscotti about 1-inch thick (I like to start by cutting the log in half, then cutting each of the 2 smaller logs in half and so on until all the pieces are uniform) and lay them cut side up on the baking sheet. Be careful-- they’re hot!
Bake the biscotti for an additional 25-28 minutes, or until they are firm and dry. Allow the biscotti to cool fully before transferring them to an airtight container.