Preheat the oven to 350°F. Line a baking pan with parchment paper or a silicone baking mat. Set aside.
In a large bowl, whisk together flour, baking powder and sea salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat together softened butter and sugar until it is light and fluffy. Add eggs one at a time, beating after each addition.
Add Amaretto liqueur, vanilla extract and almond extract to the mixture. Mix until well-incorporated.
With the mixer on medium-low, slowly add in the flour. Mix until the flour is just incorporated.
Add the sliced almonds and fold in by hand or mix gently with the mixer as to not break the pieces up too much.
Sprinkle a little bit of flour over the top of the dough and dust hands with flour. Grab about half the dough and carefully (and quickly) place it on the lined baking pan and form into a log that is about 12 inches long and 3 inches wide. Do the same with the other half of the dough, leaving about 4-5 inches between them as they will spread a bit during baking.
Bake for about 25 minutes or until they are puffed and light golden brown. Remove from oven and allow to cool for about 5-10 minutes. Turn the oven down to 250°F.
Using a serrated knife, carefully slice about 1 inch biscotti from each log. Place the biscotti, cut side down, back onto the baking pan. (I remove the parchment at this point, but you can leave it on if you prefer.)
Bake for 25 minutes, then flip and bake for another 20 minutes or until the biscotti have dried out and are crisp and golden.
Remove from oven and allow to cool completely.