Preheat oven to 350°F. Line a baking sheet with parchment paper.
Toast the slivered almonds on a dry baking sheet for 8–10 minutes, until fragrant and lightly golden. Set aside to cool.
Sift together the flour, baking powder, and salt in a medium bowl. Set aside.
Using a mixer, beat the sugar and eggs for 3 to 4 minutes, until pale and thickened. Add the almond extract.
Slowly add the flour mixture to the egg mixture, mixing just until combined.
Fold in the toasted almonds.
Form the dough into a log about 12 inches long and 1 to 1½ inches high on the prepared sheet.
Bake 20 to 25 minutes, until the log is firm and lightly golden.
Remove from the oven and cool for about 10 minutes — not longer, or the log will shatter when you slice it.
Using a serrated bread knife, slice the log into ½ to ¾ inch slices. Place cut side down back on the baking sheet.
Bake about 10 minutes per side, until golden. The longer you bake, the crisper and less chewy they become.
Cool completely on a wire rack before storing in an airtight container.