Peach Zucchini Muffins

To make the crumb topping:

1. Place the melted butter, flour, sugar, cinnamon, and salt in a medium bowl, and toss together with a fork until crumbly.

To make the muffins:

1. Preheat the oven to 425° F, and line a muffin pan with papers.
2. Place the flours, sugar, baking powder, and salt in a large bowl and whisk to combine.
3. Place the Greek yogurt, melted butter, milk, eggs, and vanilla in a separate, smaller bowl, and whisk to combine.
4. Chop the peach into a ¼-inch dice, and grate the zucchini, allowing it to drain over a bowl in a fine-mesh sieve.
5. Pour the liquid ingredients into the dry, and fold gently until almost combined (batter will be thick).
6. Fold the peaches and zucchini into the batter, until all the ingredients are just combined, but the batter is still a little lumpy (be careful not to overmix, or the muffins could come out tough).
7. Transfer the batter to the prepared pan, and sprinkle the tops of the unbaked muffins with crumb topping.
8. Bake for 5 minutes, then turn the oven temperature down to 350° F (without opening the oven door), and bake for an additional 12 to 16 minutes, or until a toothpick inserted into the thickest part of a muffin comes out clean or with a few moist crumbs.