Preheat the oven: Preheat oven to 350°F. Bake sliced and slivered almonds in a single layer in a small to medium shallow pan for 6 minutes or until toasted and fragrant, stirring halfway through. Cool completely (about 20 minutes). Reduce oven temperature to 325°F.
Process almonds: Process sliced and slivered almonds in a food processor for 30 seconds or until finely ground.
Cream butter and sugar: In a large bowl with a hand mixer, beat butter at medium speed until smooth and creamy for about 2 minutes. Gradually add almond extract, pure vanilla extract, and 1 cup powdered sugar, mixing well until fully combined.
Combine dry ingredients: Add flour and salt to the butter mixture in two additions, mixing until just combined after each addition. Stir in the toasted almonds by hand.
Shape cookies: Scoop 1 heaping tablespoon of dough and roll into balls. Place balls 2 inches apart on parchment paper-lined baking sheets.
Bake: Bake at 325°F for 12-15 minutes or until the edges are lightly browned. (I baked mine for 14 minutes but every oven is different.)
First sugar coating: Allow the cookies to cool for 5 minutes on the baking sheet. Gently roll them in the confectioners’ sugar to coat the cookie completely. Shake off any excess sugar and place the cookies on wire racks to cool completely. (Note: The sugar may melt and become slightly sticky, which is normal.)
Final sugar coating: Once the cookies have cooled completely, roll them in the confectioners’ sugar again. This is when the sugar will really stick. Shake off any excess, and the cookies are ready to eat!
Cookies stay fresh when covered at room temperature for up to 1 week.