1. Preheat oven to 350 degrees. In a medium bowl, mix flour, salt, baking powder and ground cinnamon. Set aside.
2. In the bowl of an electric mixer, mix vegetable oil and sugar on medium speed. Add eggs one at a time, mixing in between.
3. Add vanilla extract, Greek yogurt and applesauce and mix until smooth.
4. Gradually add in the dry ingredients on low speed until you have a smooth batter. Do not over mix.
5. Line the wells of a muffin pan with parchment paper liners. These are the best because they don’t stick to the cupcake.
6. Divide the batter between the 12 cups, filling them a little more than 3/4 full.
7. Bake for 20-23 minutes, or until a toothpick inserted into the center of the cupcake comes out clean.
8. Cool on a wire rack.

For the Frosting

1. Pour the sweetened condensed milk into a mason jar, cover the top of the jar with foil, set it in the center of the crockpot, and fill the crockpot with water up to the level of the sweetened condensed milk. Cover and cook on LOW for 8 hours. Allow it to cool completely.
2. In the bowl of an electric mixer, whip butter on medium high speed until it is fluffy and pale. Gradually add the sifted powdered sugar, salt, and then heavy cream. Be sure to turn the mixer down when you first add the powdered sugar and then gradually increase the speed. Once everything is incorporated, allow your mixer time to whip the frosting on high speed until it is fluffy.
3. Add 1/2 cup of the dulce de leche to the buttercream, and mix on low speed. If you would like to see swirls of dulce de leche in your piped frosting, do not mix it in completely.
4. Scoop the frosting into a piping bag fitted with an open star tip (I used Wilton 1M) and pipe onto cooled cupcakes, starting in the center and then circling around the perimeter of the cupcake. Sprinkle with sea salt if desired to enhance the caramel flavor in the frosting.