Start by preheating your oven to 350°F (175°C). This ensures that your muffins bake evenly and rise beautifully.
Spray your muffin tin with canola oil spray or another neutral oil spray to prevent sticking. Alternatively, you can line the muffin cups with paper liners for easy removal.
In a large mixing bowl, whisk together the plain flour, baking powder, cooking salt, and cinnamon powder until well combined.
In a separate bowl, whisk together the eggs, caster sugar, oil, milk, and vanilla extract until the mixture is smooth. Slowly drizzle the warm melted butter into the wet mixture while whisking.
Gently fold the wet ingredients into the dry ingredients using a spatula. Be careful not to overmix; it’s okay if there are a few lumps in the batter.
Using a spoon or a cookie scoop, fill each muffin cup about two-thirds full with the batter.
In a small bowl, mix the remaining caster sugar with the cinnamon powder. Sprinkle this mixture generously over the tops of the muffin batter.
Place the muffin tin in the preheated oven and bake for about 15-18 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the muffins from the oven and let them cool in the pan for about 5 minutes. Then, transfer them to a cooling rack to cool completely.