Preheat your oven to 375°F (190°C) and gather your mixing bowls, measuring utensils, and muffin tin.

Wash and dice the fresh strawberries into small chunks and pat them dry with a paper towel.

Melt the butter in a microwave-safe bowl or on the stovetop until liquid; cool slightly.

Sift together the muffin mix, baking powder, salt, and sugar in a large mixing bowl.

In a separate bowl, whisk together the melted butter, eggs, milk, and vanilla extract until well blended.

Pour the wet mixture into the dry mixture and gently fold together using a spatula until just combined.

Gently fold in the prepared diced strawberries, taking care not to smash them.

Fill each muffin cup in your prepared tin about ¾ full with the batter. Sprinkle coarse sugar on top if desired.

Bake for 20-25 minutes, checking for doneness by inserting a toothpick into the center; it should come out clean.

Remove muffins from the oven and let cool in the pan for about 5 minutes before transferring to a wire rack.