Heat the oven to 350°F (175°C). Line a large baking sheet with parchment. Spread the almonds on the sheet and toast until fragrant and slightly darkened, 8–10 minutes; set aside to cool slightly.
Finely zest the lemon and set the zest aside. In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In a separate bowl, whisk the eggs with the vanilla extract and the lemon zest until well combined.
Make a well in the dry ingredients and add the egg mixture. Stir with a spatula until a soft, slightly sticky dough forms. Fold in the toasted almonds until evenly distributed.
Divide the dough in half. With lightly damp hands, shape each portion into a log about 12 inches long and 2 inches wide on the parchment-lined sheet, spacing the logs a few inches apart and smoothing the tops.
Bake until the logs are pale golden, set, and show fine surface cracks, 25–30 minutes. Transfer the sheet to a rack and cool for 10 minutes. Reduce the oven temperature to 325°F (165°C).
Carefully transfer the warm logs to a cutting board. Using a serrated knife, slice on a slight diagonal into 0.5-inch-thick pieces.
Arrange the slices cut side down on the baking sheet. Bake at 325°F for 8–10 minutes, flip each slice, and bake another 8–10 minutes until dry through the center and lightly golden. Cool completely on a rack; they will crisp further as they cool.