In a bowl, whisk together the flour, baking soda, cinnamon & salt.
In a separate bowl, mix melted butter, eggs, maple syrup, brown sugar and the grated apple.
Pour apple mixture into flour and stir well.
Pour this over the apples and bake 40-45 minutes.
Let cake cool 5 minutes.
Run a knife around the edges of the cake and carefully invert the warm cake onto a large plate.
Drizzle on the reserved syrup mixture, reheating if necessary.