Let the raspberries defrost while you prepare the cupcakes. Preheat the oven to 350 degrees Fahrenheit. In a medium sized bowl, mix together the flour and salt and then set it aside. In a large bowl, cream together the cup of butter and ultrafine sugar until well blended.

Add the eggs, one at a time, mixing well after each addition. Add the vanilla extract, vegetable oil, lime zest, and lime juice and mix until combined. Gradually begin to add the flour mixture to the butter mixture, alternating with adding the whole milk and buttermilk, until the mixture is just blended.

Fill the lined cupcake tins about three-fourths full and bake for 12-15 minutes, or until a toothpick stuck into the middle of a cupcake comes out clean. Remove the cupcakes from the pan and allow them to cool for at least 30 minutes before frosting.

To make the frosting, crush the defrosted raspberries into a jelly using a potato masher. Then mix them with the butter in a large bowl until well blended. The mixture may get stuck in the mixer's whisks, like in the photo below. If that happens just turn off the mixer and use a spatula to push the mixture off the whisks and back into the bowl.

Add the powdered sugar, about a cup at a time, mixing well after each addition. When the mixture is entirely blended, it should be refrigerated for 10 minutes to help it gain back some firmness before frosting.