Preheat the oven to 180°C or 350°F, then line a 12 hole muffin tray with cupcake cases. We use 2” (50mm) cases.
Melt the margarine in a saucepan on a low heat, then add to a mixing bowl with the remaining cake ingredients. Gently mix the cupcake ingredients until fully combined.
Spoon 2 tbsp of mixture into each cupcake case or, if using different sized cases, fill until each case is roughly 3/4 full.
Bake in the preheated oven for 22-24 minutes or until a skewer comes out clean.
Remove the muffin tray from the oven and transfer the cupcakes to a cooling rack. Leave the cakes to cool completely.
Meanwhile, prepare the frosting by transferring the frosting ingredients to a mixing bowl and combining all the ingredients until smooth. If the frosting is too thick, add more milk a small amount at a time. Then transfer the frosting to a piping bag.
Pipe a generous amount of frosting onto the cupcakes and top with a sprinkling of crushed peanuts and pretzels. Finish with a single pretzel on top of each cupcake.