Apple Filling: Peel, quarter, core and slice apples. In skillet, melt half of the butter over medium heat; cook half of the apples, stirring often, until tender-crisp, about 7 minutes. Repeat with remaining apples. Scrape into bowl; mix with granulated and brown sugars, cinnamon and lemon rind. Let cool.

Cake: In bowl, whisk together cake-and-pastry and spelt flours, baking powder, baking soda and salt; set aside. In large bowl, beat eggs with sugar until pale and thickened, 2 to 3 minutes. Mix in butter, oil and vanilla. Stir in flour mixture until smooth.

Line bottom of 8-inch (2 L) square metal cake pan with parchment or waxed paper; grease sides. Spread two-thirds of the cake batter into pan. Layer apples (and juices) evenly over batter. Top with spoonfuls of remaining batter; do not smooth top. Bake in centre of 325F (160C) oven until golden brown and skewer inserted in centre comes out clean, about 50 minutes. Let cool in pan on rack. Remove from pan; peel off paper. Dust top with icing sugar.

Makes 8 to 12 servings.