Place a paper baking cup 24 cupcake wells of the muffin pan; set aside.
In large bowl, beat all cake ingredients together (except egg whites) until just combined.
Beat in egg whites for 2 minutes.
Pour into baking pan.
Bake 15 to 20 minutes or until a toothpick inserted in center of cupcakes come out clean.
Cool 10 minutes in pan before removing to a wire rack for additional cooling.
For the frosting
In a 2-quart saucepan, melt butter over medium-high heat until butter becomes a dark golden brown (amber color) with a nutty aroma, 3 to 5 minutes. Watch closely to prevent burning of the butter.
Add brown sugar and boil for 1 minute, whisk continuously. Decrease heat to medium and add 1/4 cup cream and Kosher salt.
Continue whisking for 2 minutes. Add more salt if needed.
Remove from heat and set to cool. Reserve 3 tablespoons of salted caramel in a small bowl; set aside. This will be used to drizzle on the popcorn.
Allow the remaining caramel to cool till warm to the touch.
Drop 2 cups of confectioner’s sugar in it and whisk until just combined.
Place a large dollop of frosting onto cupcakes and spread to create dome-shaped tops.
Before the frosting dries, place popcorn onto the applied frosting.
Reheat reserved caramel if necessary by heating in the microwave for 15 seconds.
Drizzle caramel on popcorn cupcakes.
Sprinkle a pinch of sea salt and serve.
Recipe Notes
When you add the confectioner’s sugar to the caramel, some brown sugar-caramel clumps may be seen which is okay. Add the remaining 1/2 cup confectioner’s sugar if needed to stiffen frosting.