01 - Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly with butter.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well blended.
03 - In a separate bowl, whisk eggs, melted butter, milk, and vanilla extract until smooth and combined.
04 - Pour the wet ingredients into the dry ingredients. Gently fold with a spatula until just combined—do not overmix or muffins will become tough.
05 - Gently fold in the diced strawberries and rhubarb until evenly distributed throughout the batter.
06 - Divide the batter evenly among the prepared muffin cups, filling each about ¾ full.
07 - Sprinkle the tops with turbinado sugar for a crunchy crust, if desired.
08 - Bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out clean.
09 - Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.