Combine slivered almonds and 1/4 cup flour in a food processor.

Process until almonds are coarsely ground.

Add remaining flour, sugar, and salt to the food processor.

Process until well combined.

Add cold butter, lemon rind, and almond extract to the mixture.

Process until the mixture begins to come together as a dough.

Divide the dough into 4 equal portions.

Shape each portion into a log approximately 1 3/4 inches in diameter.

Wrap each log tightly in plastic wrap.

Refrigerate the wrapped dough logs for at least 1 hour, or until thoroughly chilled.

Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).

Remove the chilled dough logs from the refrigerator.

Working in batches, slice the dough into 1/4-inch thick rounds.

Place the sliced rounds on a baking sheet lined with parchment paper, leaving a small space between each cookie.

Bake in the preheated oven for about 10 minutes, or until the edges of the cookies just begin to turn golden brown.

Remove from the oven and transfer the cookies to a wire rack to cool completely.