Preheat oven to 350° F and line or grease a 12 hole cupcake tin.

In a large bowl (or the bowl of a stand mixer), mix together flour, salt, baking soda, and sugar on low speed.

Add butter and mix on medium until corse crumbs form, 60 seconds or less. Mix in yogurt for a lumpy batter.

Add egg, egg yolk, vanilla, lime zest and lime juice. Beat until smooth (batter will be very thick and sticky). Add blackberries and carefully mix in using a wooden spoon or a spatula, being careful not to squish the berries.

Divide batter between cups (I used an ice cream scoop and it was a heaping scoop per cupcake, the batter is so think this is the easiest way to divide it equally). Smooth the tops (you can use an off-set spatula or I lightly sprayed the bottom of a 1/4 cup measuring cup and used that).

Bake for 20-22 minutes or until a toothpick comes out clean. Allow to cool for 5 minutes in pan then move to a wire rack to fully cool before topping with frosting.

With an electric mixer or a stand mixer, beat butter on high (with whisk attachment) for 3-5 minutes until butter is lighter in colour and doubles in volume. One cup at a time, add icing sugar (I used closer to 4 cups for this recipe). Beat in salt, lime zest, and lime juice. Finally beat in whipping cream, one tablespoon at a time until desired consistency is reached (I used 2 tablespoons).

To frost cooled cupcakes, place a small spoonful of blackberry jam or purée down the side of a pipping bag (or freezer bag). Add icing to bag and pipe* onto cupcakes in a circular motion moving upwards.