Preheat oven to 300°F. Line a large baking sheet with parchment paper.
Place the almond paste, confectioners sugar, and salt in the bowl of an electric mixer and mix until crumbly, about 3 minutes.
Slowly add egg white and vanilla. Mix until smooth and thickened about 2 minutes.
Drop batter by tablespoons onto baking sheet spacing 2 inches apart. Place 3 almond slices on each mound of dough.
Bake until cookies are golden brown, 22 - 25 minutes. Let cool completely on a wire rack. Once cool dust cookies with confectioners sugar.
Store any uneaten cookies covered for 3 days, longer in the refrigerator.