Preheat the oven to 180C/350F and line a 12 hole cupcake tray with liners.
Place the butter/margarine, lime zest and sugar into a large bowl, or the bowl of your stand mixer, and beat on medium-high speed until light and fluffy, around 2 minutes.
Add in the eggs, scraping down the sides as necessary, and mix on med-high speed until well incorporated.
Place the flour, salt (if using), baking powder and blackberry halves into a medium sized bowl and stir until all the blackberries are coated in flour. Tip this mixture into your butter/egg mixture.
Mix on low until the flour starts to incorporate and then pour in the milk. Continue mixing on low until well combined and there are no lumps of flour. Don’t mix too fast otherwise, the blackberries will become mush.
Divide the batter between your cupcake liners, filling them ¾ full. I use a 2tbsp cookie scoop to ensure evenly sized cupcakes.
Place in the oven for 18-22 minutes, until rise, lightly golden and an inserted skewer into the centre comes out clean.
Transfer the cupcakes to a wire rack to cool as soon as possible. I find that if you leave them in the cupcake tray the grease makes the liners peel away from the cake.
Once cool, make the frosting: Place the butter, icing sugar, lime zest and lime juice into a large bowl, or the bowl of your stand mixer and mix on low-medium until the sugar starts to incorporate.
Once the sugar is mixed in and can no longer create a dust cloud, turn the speed up to high and beat until light and fluffy, around 2 minutes. Frosting will become slightly paler in colour.
At this stage, if the frosting is too runny, add more icing sugar 1tbsp at a time. If it is too stiff, add more lime juice, 1tsp at a time. For me, this recipe was just perfect to pipe onto my cupcakes.
Fit a piping bag with an open star nozzle and then half fill it with frosting.
Pipe a swirl onto each cooled cupcake and then top each cupcake with a whole blackberry.
Drizzle a little blackberry coulis onto each cupcake.
Blackberry Lime Cupcakes will keep in an airtight container, in the fridge for 3 days.