Preheat your oven to 180°C (350°F). Line a muffin tin or grease it well. Skipping this step is how sadness happens.
Mix the dry ingredients. In a large bowl, whisk together flour, baking powder, cinnamon, and salt. No lumps allowed—break them up like you mean it.
Whisk the wet ingredients. In another bowl, mix sugars, eggs, oil (or butter), milk, and vanilla until smooth and glossy.
Combine wet and dry. Pour the wet mixture into the dry. Stir gently. Stop as soon as everything is combined. Overmixing = tough muffins. We don’t want that energy.
Fold in the apples. Use a spatula and a light hand. Every scoop should have apple—this is non-negotiable.
Fill the muffin cups. About ¾ full is perfect. Sprinkle a little extra cinnamon-sugar on top if you’re feeling extra (recommended).
Bake for 18–22 minutes, until a toothpick comes out mostly clean. A few moist crumbs are fine—dry crumbs are not the goal.
Cool slightly, then enjoy. Or burn your tongue immediately. Your call.