1 cup (2 sticks) unsalted butter, room temperature
1 cup confectioners' sugar
3/4 teaspoon almond extract
1/2 teaspoon salt
2 cups all-purpose flour (spooned and leveled)
Grated zest of 1 orange (about 2 teaspoons)
3/4 cup sliced almonds
In a mixer bowl, beat butter, sugar, almond extract, and salt until smooth. With mixer on low speed, add flour and orange zest; mix just until a dough forms. With a wooden spoon, rubber spatula, or your hands, gently mix in almonds.
On a piece of waxed paper, form dough into a rectangular log, 12 inches long, 2 1/2 inches wide, and 1 inch thick. Wrap log in the paper, and freeze until firm, at least 1 hour and up to 3 months. If freezing longer than 1 day, wrap log again, in plastic wrap.
Preheat oven to 325 degrees. Remove dough from freezer. (If dough has been in freezer a long time and is frozen solid, let it sit at room temperature 30 minutes so it slices without crumbling.)
With a sharp knife, cut dough into 1/4-inch-thick slices; place on ungreased baking sheet at least 1 inch apart. Bake until edges just begin to turn golden, 20 to 25 minutes. Cool 5 minutes on baking sheet; transfer cookies to a rack to cool completely.