Preheat the oven to 180°C and line a muffin tin with 12 patty cases, and a second tin with 2 patty cases.
In a small bowl combine white vinegar and dairy-free milk. Set aside.
In a medium bowl, whisk together flour, cocoa powder, bicarbonate of soda, baking powder and spices.
In a large bowl, whisk together canola oil, brown sugar, golden syrup and vanilla until combined. Add a bit of the milk mixture and whisk until combined.
Slowly add the dry ingredients to the oil and sugar mixture, alternating with the rest of the milk until cupcake batter comes together, scraping down the sides of the bowl as necessary.
Spoon mixture into patty cases ensuring they are only ½ full before placing them in the oven for 18 minutes or until lightly springy to touch. Let cool completely before frosting.
Make the buttercream frosting. Using a handheld mixer or a stand mixer with the paddle attachment fitted, beat dairy-free butter and vanilla for 1-2 minutes until creamy. Add in 3 cups of icing sugar and beat on medium until combined. As mixture thickens, add in the dairy-free milk a little at a time until the mixture is smooth and creamy but still thick enough to stand up on its own.
Separate out some of the buttercream into a smaller bowl and add a few drops of green gel food colouring until the desired colour is reached. To the rest of the buttercream add red colouring.
Decorate the cupcakes. Add the green food colouring to a piping bag with a leaf tip (such as a #66 or #70) attached and pipe 3x leaves onto each cupcake. Use the same tip in another piping bag with the red buttercream and pipe leaves around the edge of the cupcake, followed by more around the inner circle so you have 2 layers of overlapping leaves. Add a few chocolate jimmy’s to the centre and optional gold sprinkle for festive flair.