Melt the butter in a large pan set over medium-high then add the apples. Cook until the apples start to turn golden brown then sprinkle in the sugar and cinnamon.
Cook until the apples are cooked through and caramelized. Remove from the heat and allow to cool to room temperature.
Make the batter
Preheat the oven to 180°/350°F and line a cake pan with parchment paper.
Whisk the dry ingredients together in a large bowl. In a separate bowl, whisk together the eggs, yogurt, oil and milk.
Pour the wet ingredients into the dry ingredients and mix until just combined. Fold in the caramelized apples and any of the caramel in the pan.
Transfer the batter to a greased and line cake pan (I used a 20cm/7.8in square cake pan) and smooth the top.
Place in a preheated oven and bake for 30-45 minutes or until a skewer inserted comes out clean. Remove from the oven and allow to cool in the pan before turning out.
Dulce de leche whipped cream
Whip the cream with the dulce de leche until soft peaks form. Slice the cake and serve with a dollop of the whipped cream.