Preheat oven to 350°F and line your cupcake pan with cupcake liners.
Melt butter then set aside and let it cool slightly.
Combine flour, baking powder, baking soda, salt, 1 ½ cups sugar, and orange zest in a large bowl, set aside.
Whisk buttermilk, butter, oil, vanilla and egg yolks until well combined.
Using a stand mixer or electric hand mixer and the whisk attachment, whisk egg whites and cream of tartar on medium speed until foam appears (about 1 minute). Then whisk on high until the egg whites become cloud like (1-2 minutes).
Slowly add remaining ¼ cup of sugar to the egg whites and whisk until stiff peaks form (3-5 minutes). Move egg whites to a different bowl.
In the stand mixer bowl add the flour mixture. While whisking on low speed, slowly add the buttermilk mixture, then increase the speed to medium high and make sure it is fully incorporated.
Using a large spoon or rubber spatula fold in, by hand, ⅓ of the egg white mixture into the batter. Then carefully fold in the remaining egg white mixture making sure there aren’t any white streaks when done.
Pour ~ ¼ cup of batter into each cupcake liner and bake for 15 minutes or until a toothpick inserted comes out clean.
10. While the cupcakes are baking, juice an orange and mix in the sugar to make the syrup.
11. After the cupcakes are done baking, using a toothpick poke holes in the tops of the cupcakes and drizzle the orange syrup over each one.
12. Heat the marmalade in a medium-small pot over medium heat until it is runny and warm. Put a spoonful of marmalade on each cupcake before frosting.