In a small bowl, whisk together 2 teaspoons egg replacer powder with 4 tablespoons water. Set aside.
Preheat oven to 175ºC, fan forced. Grease and line a 20x20cm square pan with baking paper.
In a medium bowl, combine flour, baking powder, bi-carb soda and salt. Whisk together and set aside.
In the bowl of an electric mixer, cream together butter, brown sugar and vanilla until fluffy for approximately 2 minutes.
Add egg replacer mixture prepared in step 1 and yoghurt, mix for another 1 minute. Add flour mixture and combine with a spatula until no more flour streaks are visible.
Toss apple cubes with cinnamon and gently fold into the batter.
Spread batter into prepared pan, smooth surface with a spatula then place apple slices over the top, slightly overlapping in rows. Sprinkle extra cinnamon if desired.
Bake in oven for 35 minutes or until a skewer inserted into the centre comes out clean. Remove from oven and let slice cool in the baking tin on a wire rack for at least an hour before slicing.
For caramel sauce: In a medium saucepan, combine all the ingredients and gently melt over a low heat and bring to a simmer whisking constantly for approximately 7 minutes. Sauce will thicken further as it cools. Drizzle salted caramel sauce over the apple slice before serving.