Preheat the oven to 180 degrees Celsius / 350 Fahrenheit. Lightly oil a 20 cm / 8 inch
round cake tin and line the bottom with a round of baking paper.
Heat the butter, sugar, maple, vanilla paste, cinnamon, and lemon juice in a wide shallow pan over low-medium heat until the butter has melted. Add the apples in an even layer and allow to gently cook in the syrup for 10 minutes, stirring gently on occasion. Remove the pan from the heat and let sit until cool enough to handle. Then arrange the apples in the lined pan, making sure they are nice and snug and close to each other.
Pour the almond milk and apple cider vinegar into a measuring jug. Mix gently and leave to 'activate' for 10 minutes to create 'buttermilk'.
In a large bowl, whisk together the flours, sea salt, baking soda, baking powder and spices to combine. In a separate bowl, whisk together 'buttermilk', sugar, olive oil, yoghurt, and vanilla until smooth. Fold the wet mixture through the flour mixture until just combined (or whisk together well if using a gf flour), then spoon the batter over the top of the apples, and even it out with a spatula.
Bake on the middle rack of the oven for about 25-30 minutes, or until a skewer inserted into the middle of the cake comes out with no gooey batter attached. Remove from the oven and allow to cool for 15 minutes in the pan, then carefully invert onto a cooling rack and lift the tin off. It should slip right out, slide a knife around the edge if it needs a little help. Allow to cool completely then serve.