Add the unsweetened applesauce and vanilla extract and mix until combined.
If the dough looks too dry, add a little more applesauce or a splash of water. The batter should be thick and lumpy, but not dry.
If you'd like to use dried fruit to color the frosting, place the dried berries in a mini food processor and blend on high until they become a fine powder.
Sift them with a fine mesh sieve, discarding any larger crumbs. Set the powder aside.
Once the cookie bars are cool, make the frosting. Beat the vegan buttery spread until fluffy, then sift in about a ½ cup of sifted powdered sugar. Mix until combined, then alternate adding more sifted powdered sugar and a little water. Add the powdered berries if you are using them. I used about 1 ½ Tablespoons of dried blueberry powder to achieve the color in the photos.
Allow the bars to cool fully before frosting and slicing.
You don't have to frost these - you could drizzle melted chocolate on top, or dust with powdered sugar, or place sliced strawberries on top. This is a very versatile recipe.
Store cookie bars in an airtight container. They should stay fresh for 3-4 days.