Preheat the oven to 325 degrees F, and line cupcake tins with papers.

Place the flours, brown sugar, cinnamon, baking powder, baking soda, and salt in a large mixing bowl and whisk to combine.

Place the oil, apple cider, eggs, vanilla, and lemon zest in a large liquid measuring cup, and whisk to combine.

Pour the liquid ingredients into the dry, and mix together on medium speed for about 1 minute.

Fold in the shredded apple.

Divide the batter equally between all 18 lined wells of the cupcake tin.

Bake for 18 to 22 minutes, or until a toothpick inserted in the thickest part of a cupcake comes out clean or with a few moist crumbs.

Cool completely before topping and garnishing.

In a small pot, gently heat the cream, butter, and salt until the butter has melted and the salt has completely dissolved.

Remove from heat and add the vanilla.

In a larger pot, combine the sugar, corn syrup, and water. Heat over a medium high flame, swirling the pot occasionally to distribute the heat evenly.

Continue to boil the sugar mixture until the bubbles begin to get smaller and it becomes amber-colored.

Reduce the heat to low, and pour in the warm cream mixture, whisking constantly to avoid lumps or crystals.

Immediately transfer the hot mixture to a heat-safe vessel and cool completely.

Place the butter, powdered sugar, and additional salt (if using) in a large mixing bowl and whip together until pale and very fluffy.

Add about 3/4 of the cooled caramel sauce, continuing to whip until well incorporated.

Transfer the caramel buttercream to a pastry bag fitted with a jumbo open star tip.

Pipe the buttercream onto the cooled cupcakes, drizzle with the remaining caramel sauce, and top with chopped peanuts.