Start by positioning a rack in the center of your oven and preheating to 400°F. While the oven heats, generously grease a standard 12-cup muffin tin with softened butter. Don't skip this step or use cooking spray—the butter creates a beautifully browned edge that's one of the hallmarks of these muffins. If you're doubling the recipe, prepare two tins now. This initial step takes just three minutes but sets the foundation for success.

In a large mixing bowl, whisk together the all-purpose flour, whole wheat flour, baking powder, salt, and nutmeg. Whisk for about 20-30 seconds to fully incorporate the leavening agent—this distributes the baking powder evenly so you don't end up with pockets of dense muffin. Set this bowl aside. This is a critical step that many home cooks rush through, but it takes less than a minute and makes a genuine difference in your final product.

In a medium bowl, whisk together the melted butter and maple syrup until fully combined. The mixture should look like liquid amber—glossy and smooth. Add the vanilla extract and whisk again. Now, slowly add the milk while whisking, then add the whole egg and egg yolk. Whisk until the mixture is completely smooth and uniform. This step takes about two minutes and is genuinely important for even distribution of moisture throughout your muffins.

Pour the wet mixture into the dry ingredients and whisk gently just until you see no white streaks of flour—this should take about 15-20 whisks. I know the temptation is to mix until everything looks perfectly smooth, but resist it. Overmixing develops gluten, which turns muffins dense and tough. The batter will look slightly lumpy, and that's exactly what you want. Stir in the walnuts with just a few gentle folds. Let the batter rest for 5 minutes—this allows the whole wheat flour to fully hydrate, which improves moisture and texture dramatically.

Using a ice cream scoop or large spoon, divide the batter evenly among the prepared muffin cups. Fill each cup until it's nearly full—these muffins will rise beautifully and you want that gorgeous dome. Place the tin in your preheated 400°F oven and bake for exactly 10 minutes. At the 10-minute mark, reduce the temperature to 375°F and continue baking for approximately 15 minutes more, until the muffins are golden brown on top and a cake tester or toothpick inserted into the center comes out clean. The whole process from start to finish should take about 35 minutes.

Allow the muffins to cool in the pan for exactly 5 minutes—this helps them set enough to remove without crumbling, but they're still warm enough to taste incredible. Gently run a thin knife around the edges of each muffin to release them from the pan, then lift them out carefully. Serve them warm with softened butter, or transfer them to a cooling rack if you're serving them later. Warm maple muffins with butter are honestly one of my favorite simple pleasures in the kitchen.