In a medium saucepan, combine the sugar, salt, cream of tartar, and water.

Heat over medium high heat, stirring often with a rubber spatula to encourage even cooking.

When it comes to a boil reduce heat to medium and continue stirring often.

When the color turns an even medium amber color remove from heat and add the heavy cream, quickly mixing until fully combined.

Then, mix in the butter and vanilla.

Transfer to a glass jar to cool, stir in a pinch or two of flaky sea salt, then chill in the fridge overnight or until ready to use.

Preheat the oven to 350 degrees F.

Start by browning the butter. You'll need 84g of brown butter, so start with about 113g.

To brown the butter, in a small saucepan, heat the butter over medium heat for several minutes, swirling to even out the color. The butter will be ready once the fat solids have separated and darkened, and the butter is an even medium amber color.

Pour the brown butter into a large mixing bowl and place in the fridge to chill for 15 minutes.

Meanwhile, switch over to making the spiced caramel apples.

In a glass measuring cup, stir together the caramel sauce and spices. Set aside.

Place a 9" cast iron skillet over medium heat.

Add the butter and stir frequently until the milk solids have separated and browned.

Add in the thinly sliced apples and brown sugar, and stir often for about 3-4 minutes.

Drain the apple juices from the skillet, then pour the spiced caramel sauce over the apples and cook for another 2 minutes, stirring often.

Remove from heat and allow to cool.

Meanwhile, finish making the cake batter.

In a small bowl, combine the flour, baking powder, baking soda, salt, and spices.

To the cooled brown butter, whisk in the brown sugar, then the egg and vanilla.

Add in half of the dry ingredients, and mix until just combined.

Whisk in the applesauce and buttermilk.

Then, mix in the rest of the dry ingredients until just combined.

Pour the cooled spiced caramel apples into the cake batter and mix with a rubber spatula until evenly dispersed.

Pour the batter back into the cast iron skillet and smooth out the top.

Sprinkle with turbinado sugar and bake for about 35 minutes or until a toothpick inserted comes out clean.

Allow to cool for about 20 minutes, then drizzle more caramel sauce on top.

Enjoy warm with a big scoop of vanilla ice cream!