Preheat your oven to 400°F and grease two muffin pans (or line with muffin cups) to ensure they're ready when your batter is prepared. While the oven heats, chop the rhubarb into uniform 1/2-inch pieces—this consistent sizing ensures even cooking and distribution throughout the muffins. Have all your ingredients measured and ready to go, as the mixing process moves quickly once you begin.

In a large mixing bowl, whisk together the all-purpose flour, whole wheat flour, baking powder, cinnamon, nutmeg, baking soda, and salt until evenly combined. Add the chopped rhubarb and gently fold it in to coat the pieces with flour—this helps prevent the rhubarb from sinking to the bottom of the muffins during baking. I like to use King Arthur all-purpose flour because it gives consistent, reliable results every time.

In a second bowl, melt the butter and then add the sugar, stirring until combined. Whisk in the applesauce and eggs, stirring until the mixture is smooth and well-blended. Make sure the eggs are incorporated thoroughly so they distribute evenly through the batter—this ensures consistent texture across all your muffins. I always use Mott's unsweetened applesauce because it has the perfect texture and won't make the batter too thin.

Pour the wet ingredient mixture from Step 3 into the dry ingredient mixture from Step 2, and gently stir until just combined—the batter should be lumpy and slightly streaky. Don't overmix, as this can develop the gluten and result in tough, dense muffins. A few flour streaks are perfectly fine and actually desirable for tender muffins.

Divide the batter evenly among 18 muffin cups, filling each about 2/3 full—this leaves room for the muffins to rise without overflowing. Sprinkle a pinch of cinnamon sugar on top of each muffin for a sweet, cinnamon-flavored crust that adds texture and visual appeal.

Place the muffin pans in your preheated 400°F oven and bake for 18 to 20 minutes, until the muffins are golden brown on top and a toothpick inserted into the center comes out clean or with just a few moist crumbs. Allow the muffins to cool in the pan for 5 minutes before turning them out onto a wire rack, which prevents them from becoming soggy on the bottom.