Preheat & Prep: Preheat your oven to 375°F (190°C). Line a muffin tin with liners or grease it well. Muffins hate sticking almost as much as we do.
Mix Dry Ingredients: In a large bowl, whisk together flour, sugar, baking powder, and salt. Break up any flour clumps like you mean it.
Mix Wet Ingredients: In another bowl, whisk eggs, melted butter (or oil), milk, and vanilla until smooth. This should look friendly, not aggressive.
Combine: Pour wet ingredients into dry and gently fold until just combined. Lumps are fine. Overmixing is not.
Add Fruit: Fold in mango and pineapple gently. You want fruit chunks, not tropical mush. Pro tip: Toss fruit in a little flour to prevent sinking.
Bake: Divide batter evenly into muffin cups. Sprinkle tops with coarse sugar if using. Bake for 18–22 minutes, until golden and a toothpick comes out clean.
Cool (Briefly): Let muffins cool for 5–10 minutes before diving in. Or don’t. I won’t judge.