Preheat your oven to 425°F and grease your muffin pan thoroughly with butter or cooking spray—this prevents sticking and ensures even browning on the muffin bottoms. While the oven preheats, prepare your ingredients: mash the bananas until completely smooth with no lumps (this ensures even moisture distribution), dice the strawberries into roughly ¼-inch pieces, and make sure your egg, butter, and yogurt are all at room temperature—cold ingredients won't blend smoothly and can create dense spots in your muffins.

In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Whisking (rather than just stirring) helps distribute the leavening agents evenly throughout the flour, which gives you consistent rise and crumb structure. Set this mixture aside—you'll fold it into the wet ingredients shortly.

In a separate large bowl, whisk together the melted butter and both sugars until well combined—the mixture should look slightly granular but uniform. This combines your fats and sweeteners, which creates a foundation for moisture. Add the room-temperature egg and whisk vigorously for about 30 seconds until slightly lighter in color, then stir in the vanilla extract and yogurt. The yogurt adds tanginess and moisture that keeps these muffins tender; I prefer using Stonyfield organic because it has a richer, creamier texture that really enhances the final result.

Add the dry ingredient mixture from Step 2 to the wet mixture from Step 3, then fold together gently with a spatula until just combined. Overmixing develops gluten and creates tough, dense muffins, so stop as soon as you see no streaks of dry flour—a few small lumps are perfectly fine and actually desirable.

Gently fold the mashed bananas from Step 1 into the batter, then carefully fold in the diced strawberries. This final fold should be done very gently—you want the fruit distributed throughout without breaking down the berries or creating a dense batter. Divide the batter evenly among the muffin cups, filling each about ¾ full. I like to use an ice cream scoop for this because it ensures consistent sizing and fill level, which means all your muffins bake evenly.

Place the muffin pan in your preheated 425°F oven and bake for exactly 5 minutes—this initial high heat creates lift and helps set the tops of the muffins. Then reduce the oven temperature to 350°F and continue baking for 15 more minutes, until a toothpick inserted into the center of a muffin comes out clean or with just a few moist crumbs. The two-temperature method prevents the tops from browning too quickly while the centers cook through.

Let the muffins cool in the pan for 10 minutes—this allows them to set up enough to handle without falling apart. Then turn them out onto a wire rack to cool completely. Enjoy them warm or at room temperature; they'll stay fresh in an airtight container for 3-4 days.