To prepare the cupcakes, preheat the oven to 350°F/180°C. Place paper cupcake liners in a 12-c. cupcake pan.
In a small bowl, combine the cocoa and the boiling water, stirring with a fork or whisk until smooth. Set aside to cool.
In the bowl of an electric mixer fitted with a flat paddle, cream together the butter, sugar, eggs, and vanilla extract until light and fluffy, about 5 minutes.
In a separate bowl, combine the flour, baking powder, baking soda and salt.
Begin adding the flour mixture to the creamed ingredients alternately with the cocoa mixture, beating in between each addition on low speed until ingredients are mixed together. Be careful not to overbeat.
Pour the batter into the lined cupcake pan and bake until the cupcakes spring back when touched lightly in the center, about 20 minutes.
Remove from the oven and allow to cool in the pans for about 10 minutes before removing the cupcakes from the pan to cool completely on wire racks before frosting.
To prepare the frosting, cream the butter, salt and vanilla extract together until smooth in a mixing bowl.
Start adding the sugar gradually, allowing the butter and sugar to cream together before adding more, scraping down the sides as you go. The mixture should look a little dry at this point.
Add the strawberry preserves and mix together, scraping down the sides of the bowl with a spatula to incorporate completely.
Start adding the milk, 1 Tbsp. at a time and beat on medium-high speed until you get a creamy, spreadable texture.