Gluten Free Butter Tart Bar

2 eggs 
3/4 cup (175 mL) corn syrup 
2 tbsp (25 mL) cornstarch 
1/2 tsp (2 mL) gluten-free baking powder
1/4 tsp (1 mL) salt 
1 cup (250 mL) raisins 
1/2 cup (125 mL) walnuts, chopped 
Base:
1/2 cup (125 mL) butter, softened 
1 cup (250 mL) rice lour 
1/3 cup (75 mL) tapioca starch 
1/3 cup (75 mL) packed brown sugar
2 tbsp (25 mL) potato starch 
1 tsp (5 mL) xanthan gum


Line 9-inch (2.5 L) square metal cake pan with parchment paper; set aside.
 In bowl, beat butter until fluffy. In separate bowl, whisk together rice flour, tapioca starch, brown sugar, potato starch and xanthan gum; stir into butter. Press into prepared pan. Bake in centre of 350F (180C) oven until set but not browned, about 10 minutes. Let cool in pan on rack.  Meanwhile, in bowl, beat eggs; beat in corn syrup. In separate bowl, whisk together cornstarch, baking powder and salt ; stir into egg mixture just until combined. Stir in raisins and walnuts.  Pour over base. Return to oven and bake until almost firm, 30 to 35 minutes. Let cool in pan on rack. Cut into squares. (Make-ahead: Layer between waxed paper in airtight container and store at room temperature for up to 1 week or freeze for up to 2 weeks.)Tip: The shortbread base tends to crumble if cut into bars while still warm. For easier cutting, refrigerate overnight first.