Brown Butter Crumble:

1. Preheat oven to 350F (conventional / no fan) and prepare a 9″ cake pan with parchment paper
2. Place the butter in a nonstick pan and melt over medium-low heat. Continue to cook and stir until the butter becomes brown – it will become frothy and bubbly first, but keep stirring until you see brown bits in the butter and it smells very nutty. Do not overcook as it can burn easily
3. Add the flour, brown sugar, cinnamon and salt to a bowl, and whisk until combined and no lumps remain
4. Pour in the browned butter. Use a spoon to mix the butter into the dry ingredients gently. It will become crumbly as you do this; do not overmix, only mix until no dry streaks of flour remain
5. Place in the fridge 

Cake:

1. Add the sugar, melted butter and oil to a bowl and whisk for 2-3 minutes. It’s ok if the sugar doesn’t fully dissolve
2. Add the vanilla and eggs, and whisk for another 2 minutes so until the mixture becomes smooth, caramel-y and lighter in color
3. Add the sour cream and whisk until it is combined. Scrape your bowl, if needed
4. Sift in the flour, salt, baking powder, and baking soda. Whisk very gently until just combined and no lumps remain; do not overmix

Cinnamon Apples:

1. Cut the apples into small cubes and toss with cinnamon in a bowl

Assembly and baking:

1. Spread the cake batter in the prepared 9″ cake pan
2. Top with a layer of the cinnamon apples
3. Bring the crumble out of the fridge and use your hands to spread it on top of the apples. It should be in chunks, and doesn’t have to be perfect! I like to save a little crumble, thinly slice some apples and add to the pan for decoration before sprinkling over the remaining crumble (see images in blog post above)
4. Bake at 350F for ~50-55 minutes. Test with a toothpick inserted in the middle at the 45 minute mark; it should have light crumbs but no wet batter. If the crumble is becoming too dark, you can cover the pan with aluminum foil as the cake continues to bake
5. Let the cake rest in the pan for 30 minutes before carefully taking it out
6. If adding icing, mix the sugar and cream / milk to your desired consistency and drizzle on top of the cake with a whisk or spoon
7. Slice & serve!