Preheat oven to 200C / 400F

Grease a 11×16 sheet pan with non stick spray or parchment paper. (You can also use other sizes of sheet pans such as 12×17 and 13×15) Or 9×13 for thicker cake.

FOR THE CAKE:

In a large saucepan over medium heat stir together butter and water until melted and combined. Bring to a boil and then take off the heat and let cool down for 2-3 minutes.

Meanwhile combine together flour, baking soda, granulated sugar, brown sugar and cinnamon in the bowl of a stand mixer.

Add the butter mixture to the flour mixture. Mix to combine.

Then mix in milk, eggs and vanilla extract until everything is well combined.

Carefully fold in the sliced apples with a spatula.

Pour the cake batter evenly into the prepared sheet pan.

Bake for 20-22 minutes or until a toothpick inserted into the center of the cake comes out clean or with very few crumbs on it.

Let the cake cool down while you make the sauce.

FOR THE SAUCE:

Stir together brown sugar, butter and cream in a small saucepan over medium high heat. Bring to a boil and let boil for 2 minutes until all of the sugar has dissolved and stirring frequently.

Remove from heat and stir in vanilla and sea salt.

Let the caramel cool down in the pan for about 5 minutes until it has thickened slightly. Stir frequently.

Drizzle the salted caramel sauce over the cake with a spoon and serve.