1. Preheat oven to 350 F. Line a 12-tin muffin pan with cupcake liners and set aside.
2. In a medium mixing bowl, whisk together flour, cornstarch, baking powder and salt. Set aside.
3. In a large mixing bowl, use a hand mixer or stand mixer with the paddle attachment to cream together the butter and sugar until light and fluffy, about 2-3 minutes. Add eggs, one at a time, and beat until incorporated. Add vanilla and yogurt, beating until combined. 
4. Add one-third of the dry ingredients and beat until just combined. Then, add half of the milk, and beat until just combined. Repeat, until you end with the dry ingredients. Scrape down the bowl as needed and beat until just combined and smooth. Do not overmix. The batter will be thick.
5. Use a medium cookie scoop to scoop up the batter and into the cupcake liners, filling them 2/3 full with batter. Bake for 18-20 minutes, until a toothpick inserted into the center of the cupcake comes out clean.
6. Allow the cupcakes to cool in the muffin pan for 5 minutes, then transfer into a wire cooling rack to cool completely before icing.

Decorate the Cupcakes with Buttercream:

1. In a large mixing bowl, beat the butter using a hand mixer or stand mixer on medium speed until creamy. Add vanilla and beat until light and fluffy. Add in confectioners' sugar one cup at a time and continue to beat until incorporated. Add milk ad beat until light and fluffy. Cover the bowl with a damp cloth until you are ready to use the icing to prevent it from drying out.
2. Use a couplers to secure a no. 2D decorating tip onto a piping bag. Fill the bag with icing and pipe the icing onto each cupcake starting at the edges and move in an overlapping circular motion until you reach the center and gently lift up.