Preheat the oven to 200°C (approximately 400°F). Mix the egg substitute powder with 80 ml (approximately 1/3 cup) water and let rehydrate. Meanwhile, line the bottom of a springform pan with parchment paper. Cream the margarine, sugar, salt and vanilla sugar until fluffy. Gradually add the egg substitute and continue beating until frothy. Fold in the flour and baking powder then stir in the coconut milk until just combined. Transfer to the prepared pan.
Peel the apples, quarter and core. Halve the apples again and arrange in the dough, pushing in lightly. Bake for about 45 minutes, or until a toothpick inserted in the center comes out clean. Remove from the oven, immediately sprinkle with powdered sugar, let cool for 10 minutes and then release from the springform pan. Let cool on a wire rack.