Mix the pie crust ingredients in a food processor until the dough comes together. Press into the bottom and slightly up the sides of a tart pan.
Process 2 cups of the slivered almonds and the sweetener in the food processor for 5 minutes, scraping down the sides occasionally. Add the egg whites and almond extract. Process until it comes together and is about the consistency of peanut butter. Spread onto the prepared crust using wet hands. Sprinkle the slivered almonds on top and press down lightly.
Bake for 20 minutes until slightly golden and firm to the touch. Cool completely before removing the sides of the pan. Serve with fresh berries or jam.