Line a 12 x 16 quarter sheet pan with parchment paper. (I spray the edges also.)
Mix the dry ingredients together in a medium bowl.
Mix the vanilla and buttermilk together in a small bowl.
In the bowl of your stand mixer (or by hand) cream together the butter and sugar until light and fluffy.
Add the eggs and mix to combine.
Alternate adding the wet and dry ingredients, beginning and ending with dry.
Gently mix in the grated apple.
Spread the batter on the prepared sheet pan, using an offset spatula to reach the corners if necessary.
Bake for about 25 minutes, or until fully cooked. A skewer poked in the center can have a few moist crumbs but not wet batter. Start checking the cake after 20 minutes.
Let cool and top with caramel sauce, if desired.
For the Salted Caramel Sauce
Heat the sugar in a medium pan over medium heat, stirring with a wooden spoon. It will begin to melt, then clump, and then melt again. Stop stirring once it melts.
Cook the sugar until it's amber in color, making sure not to burn it.
Add the butter, stirring to combine, being careful as it will bubble up and splatter and can burn you.
Slowly add the cream. Boil for one minute, then remove from heat and add vanilla.(If the caramel seems like it's separated at this point, just keep heating and stirring and it will come back together.)
And ½ - 1 teaspoon of salt stirred into the caramel, or use Fleur de Sel as garnish on your dessert for a salted caramel. (Omit salt completely if you prefer.)
Video
Notes
temperature: Use room temperature eggs and butter when making this cake for an even batter and butter that will cream well with the sugar.
creaming: be sure to cream the butter and sugar until the mixture is light and fluffy for a light cake.
mixing: don't overmix or you'll have a tough cake.
let cool: let the cake cool completely before adding the caramel sauce. Pouring caramel sauce onto a warm or hot cake will make the caramel sauce melt into the cake and you'll have a soggy mess.
cook time: Baking this cake batter in a large sheet pan means the cake will be thinner and won't take as long to cook. Start checking after 20 minutes. The cake shouldn't take longer than 25 minutes. Check with a skewer - a few moist crumbs are fine, but wet batter on the skewer is not.