Adjust an oven rack to the center of the oven. Preheat the oven to 350 degrees F. Line two rimmed baking sheets with parchment or a nonstick baking mat. Spray lightly with cooking spray.
Combine the almond butter, sugar, egg whites, flour, baking soda, vanilla and 1/4 teaspoon salt in the bowl of a standing mixer fitted with a paddle attachment. Beat the mixture together until well combined, about 3 minutes. Adjust the mixer to low speed and add the slivered almonds. Mix until just incorporated.
Use a rounded tablespoon to drop the dough on the prepared sheet trays, leaving at least 2 1/2 inches of space between each cookie. The batter will spread as it bakes. Place in the oven and bake until puffed and golden, 10 to 12 minutes, rotating the baking sheets about half way. Cool on the sheets for 10 minutes then cool completely on a rack.