Bring apple juice to a boil in medium saucepan over medium-high heat. Cook, stirring occasionally until reduced to ½ cup, about 15-20 minutes. Remove from heat and allow to cool to room temperature.
Preheat oven to 350°F and grease a 13” x 9” baking pan with nonstick cooking spray. Line baking pan with parchment paper sling, pushing parchment into corners and up sides of pan. In a large bowl, whisk flour, cinnamon, baking soda, nutmeg, all-spice and salt together until combined. In a separate large bowl, whisk reduced apple juice, sweetener and oil spread together until combined. Mix in eggs and vanilla until smooth. Fold in flour mixture until just combined.
Pour batter evenly into prepared baking pan. Bake until a toothpick inserted into the center comes out clean, about 35-40 minutes.
Drizzle glaze over cooled blondies. Slice into 24 squares and serve.
To make the glaze:
Add sweetener and cornstarch to blender. Blend until sweetener is a very fine powder. Add water and vanilla and blend until smooth.