Heat oven to 350°F. Line a sheet tray with parchment.
Whisk flour, baking powder, and salt in a bowl.
In a separate large bowl, cream butter and sugar until light, 3-4 minutes. Add eggs one at a time, then vanilla and almond extract.
Add dry ingredients to wet and mix until just combined. Stir in almonds (or your mix-in of choice).
Divide dough in half and form into two logs, about 10" x 3". Flatten slightly.
Bake 25–30 minutes until golden and set. Cool 10 minutes.
Slice into ¾-inch pieces with a serrated knife, cutting on the bias.
For the second bake:Oven: lay slices cut-side down and bake 10 minutes, flip, then bake another 8–10 minutes.Air fryer: place slices in a single layer at 350°F for 5 minutes. Check for crunch; add 1–2 minutes if needed. Cool completely on a rack (they will firm as they cool). Consume within 3-4 days for maximum texture.