In a small heavy-bottomed saucepan, combine water, the Redpath® Golden Yellow Sugar, and the chopped mint. Place over medium-high heat and bring to a boil, stirring to dissolve sugar. Reduce heat to low, simmer for 1 minute. Cover and remove from heat.
Allow to steep and cool completely; 30 minutes. Strain the simple syrup through a fine-mesh sieve; discard solids. If using, stir rum (see Chef’s Tips) into the cooled syrup.
Preheat oven to 325°F (163°C). Line a muffin tin with paper liners.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In the bowl of a stand mixer using the paddle attachment, cream together the butter, the Redpath® Golden Yellow Sugar, and the Redpath® Granulated Sugar until smooth and fluffy; about 3 minutes.
Add the eggs, one at a time, beating well after each addition. Scrape down the bowl as needed.
Add in the lime zest, finely chopped mint, and vanilla extract. Mix until well combined.
Add in ⅓ of the flour mixture; mix until just combined. Add in ½ of the buttermilk; mix until just combined. Repeat with the remaining flour and buttermilk, ending with the flour mixture; do not overmix.
Fill liners ¾ full. Place tin into the preheated oven. Bake for 20 to 25 minutes. Let cupcakes cool in pan before carefully removing; 5 minutes. Place cupcakes onto a wire cooling rack.
Using a pastry brush, brush the slightly cooled cupcakes 1 or 2 times with the cooled mint simple syrup.
Allow cupcakes to cool completely.
In a medium heavy-bottomed saucepan over medium heat, whisk together the flour and salt until no lumps remain, and the flour is warm; 1 minute.
Slowly stream in the milk while whisking constantly to create a smooth mixture. Continue to whisk and cook the mixture until it begins to simmer. Once it begins to bubble, cook and whisk for a minute until mixture is thick. Turn off heat and whisk in the Redpath® Golden Yellow Sugar until sugar is dissolved and mixture is well combined.
Transfer and spread the mixture into a medium shallow dish. Place a piece of parchment paper or plastic wrap directly onto the surface of the mixture. The parchment paper helps to prevent a skin from forming as it cools. Cool completely or to room temperature (see Chef’s Tips).
In the bowl of a stand mixer with the paddle attachment, cream butter on medium speed until smooth. Increase speed to medium-high and beat until pale and fluffy; about 3 to 5 minutes.
Reduce the speed to medium and gradually beat in the room temperature flour mixture about two tablespoons at a time, waiting until fully incorporated before adding the next portion.
Once all the flour mixture has been incorporated, scrape down the sides of the bowl and paddle attachment with a rubber spatula. Switch to the whisk attachment and add in the lime zest, chopped mint, and vanilla extract. Mix on low speed to incorporate the additions, then increase speed to medium-high and beat until smooth and fluffy; about 3 minutes.
Transfer the frosting to a piping bag fitted with a star or round tip (see articles “Simple Decorating Techniques Using an Open or Closed Star Tip” & “Simple Decorating Techniques Using a Plain or Round Piping Tip”).
Decorate completely cooled cupcakes with the frosting using the piping bag. Alternatively, simply dollop some frosting onto the top of each cupcake and use an offset spatula or spoon and flatten or create a slight divot by making a circular motion in the centre of the frosting, pushing the frosting to the edges of the cupcake. If desired, garnish with fresh mint leaves, lime, and/or lime zest.
*Ensure all ingredients and/or components are at room temperature before proceeding with the recipe.
*Any rum can be used in this recipe; traditionally, white rum is used in mojitos, but dark or spiced rum can also be used.
*The cooked flour mixture for the ermine frosting can be made several hours in advance or the day before. If making the day before, place the covered mixture into the fridge. Remove from fridge and allow to come to room temperature before making the frosting.
*To quickly cool down the flour mixture of the ermine frosting, transfer mixture into a larger dish where the greater surface area and thinner mixture allow it to cool faster. Or allow mixture to cool at room temperature for 10 minutes before placing the covered mixture into the fridge to chill; 15 minutes. Ensure the mixture is not too cold when adding to the butter.