1. Preheat oven to 350ºF. Line an 8” square baking pan with foil, leaving enough foil over the edges of the pan to pull the bars out once baked.

Crumble Topping

1. Whisk together the brown sugar, granulated sugar, cinnamon, and salt in a bowl. Add the melted butter and whisk in until well-incorporated. Fold in the flour until it is completely incorporated into the mixture and the dough comes together in a ball; you may need to use your hands to finish clumping all the dough together. Set aside while preparing the remaining recipe components.

Cinnamon Sugar Filling

1. In a small bowl, whisk together the granulated sugar, brown sugar, and cinnamon until evenly combined. Set aside.

Peach Layers

1. In a medium bowl, toss the peaches with the butter, flour, and cinnamon until evenly coated. Set aside.

Coffee Cake

1. In a large bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt until evenly combined.
2. In a separate bowl, whisk together the oil, brown sugar, and granulated sugar until well-combined. Add the eggs one at a time, beating in until smoothly incorporated into the batter. Add the yogurt and vanilla and beat in until smooth.
3. Add the wet ingredients to the dry and fold in just until no dry streaks are visible; do not overmix.
4. Transfer half of the batter to the prepared pan (be sure to divide the dough as evenly as possible; weigh it if you can) and use an offset spatula to smooth out in a flat, even layer that reaches all the way to the corners of the pan. Add half of the peaches on top, spread out in a single layer (again, weigh to divide if possible), and press into the batter lightly - just enough to form a semi-flat layer (this will make spreading the next layer of batter easier). The peaches should still be very visible. Sprinkle the cinnamon sugar filling evenly over the peaches; they should be almost entirely covered, if not entirely. Dollop the remaining batter over the cinnamon sugar filling, dispersing the dollops around the pan. Spread out to cover the cinnamon sugar in a flat, even layer that reaches all the way to the corners of the pan. Add the remaining peaches over the second layer of batter, again spreading out in a single layer; do not press this layer of peaches in. Crumble the crumble topping over the peaches to cover entirely in an even layer. You’ll end up with some fine crumbs, but make sure you have a good amount of large, coarse crumbs as well, pressing chunks of the dough together if needed to form larger crumbs.
5. Bake coffee cake in the preheated oven for 1 hour and 20-25 minutes, until a toothpick inserted all the way down into the center of the coffee cake comes out clean. Place pan on a wire rack and allow coffee cake to cool completely. Once cool, use foil to lift coffee cake from pan. Slice into squares with a large serrated knife. Store in an airtight container at room temperature. Pieces of coffee cake can be reheated in the microwave for 15-20 seconds, if desired.