Heat oven to 350°F (175°C). Line a rimmed baking sheet with parchment. Whisk flour, baking powder and salt together.

Beat butter and sugar until smooth and slightly lighter, about 2 minutes. Beat in eggs one at a time, then vanilla and almond extract. Stir in dry ingredients just until combined, then fold in sliced almonds. Dough will be soft and a little sticky.

With lightly damp hands, divide dough into two logs about 10 inches long and 2 inches wide, leaving at least 4 inches between them on the tray. Flatten the tops gently. Avoid adding handfuls of flour to sticky dough.

Bake 25–30 minutes, until set with lightly golden edges. Cool on the tray for 20 minutes. Reduce oven to 300°F (150°C). The short cooling period helps the logs slice without crumbling.

Transfer each log to a board. With a serrated knife and gentle sawing motion, cut into about 12 slices, roughly 3/4 inch thick. Lay slices cut side down on the lined tray. Handle gently while still warm.

Bake 12–15 minutes, turn slices over and bake another 10–12 minutes until dry and lightly golden. Cool on a rack for about 40 minutes; they crisp further as they cool. The planned cooking time rounds the two baking stages to 55 minutes.