Preheat oven to 350*F and fill a muffin tin with cupcake liners. In a small bowl, combine dry ingredients, stirring until well mixed.
In a stand mixer with a paddle attachment, beat eggs and sugar on medium speed 4-5 minutes. Slowly add in olive oil in a slow drizzle until mixture thickens and is combined. Add vanilla and mix together until blended. Add dry ingredients alternately with buttermilk to wet and stir until just combined - careful not to over mix.
Pour into muffin liners, ¾ full. Bake for 18-22 minutes, or until cake tester comes out clean. Remove to a baking rack and cool for 20 minutes before frosting.
Beat together in a stand mixer butter and cream cheese until well blended, about 3-4 minutes. Add in vanilla, balsamic vinegar and fleur de sel, beating until combined. Slowly add in icing sugar ½ cup at a time until evenly blended - use less for a softer icing, and at least 3 cups or more for a piped frosting that will hold it'?s shape.
Decorate your cooled cupcakes by spreading or piping on cream cheese frosting then adding your favorite Halloween candy!
Notes
Decorate with your favorite Haloween candies and chocolates – assuming you have any left!