Preheat your oven to 350°F and grease a 9x5 inch loaf pan or 8x8 inch baking dish with butter or cooking spray. While the oven heats, make the crumb topping by combining the brown sugar, flour, and cinnamon in a small bowl. Add the cold butter cubes and use your fingertips to work the mixture until it resembles coarse breadcrumbs with pea-sized pieces of butter throughout. Set the topping aside—having it ready before you start the batter ensures you won't have idle time later.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Make sure the baking soda and baking powder are fully distributed throughout the flour to ensure even leavening. Set this dry mixture aside—you'll combine it with the wet ingredients in the next step.

In a large bowl, whisk together the room-temperature egg, sugar, oil, sour cream, milk, vanilla, and almond extract until smooth and well combined. The sour cream adds richness and tender crumb, so make sure it's fully incorporated into the wet mixture rather than leaving streaks. Take your time whisking to create an emulsion between the oil and the dairy components.

In a small bowl, toss the diced peaches with the sugar, cinnamon, and cornstarch. The cornstarch will absorb excess moisture from the peaches as they bake, preventing a soggy center in your quick bread. Let this sit for a minute while you finish the batter preparation.

Pour the wet ingredient mixture from Step 3 into the bowl with the dry ingredients from Step 2. Gently fold together with a spatula until just combined—do not overmix, as this will develop gluten and create a tough, dense bread. Spread half of the batter into your prepared pan, then scatter the peach filling from Step 4 evenly over the batter. Top with the remaining batter, spreading it gently to cover the peaches. I like to use a gentle hand when spreading so I don't disturb and compress all those peaches—you want them distributed throughout the final bread.

Using a butter knife or small offset spatula, gently swirl through the batter a few times to create a marbled pattern and distribute the peaches more evenly—swirling also creates pockets of peach flavor throughout the bread. Sprinkle the crumb topping from Step 1 evenly over the surface, distributing it so you get crumbles in every bite.

Bake at 350°F for 60–65 minutes, until a toothpick inserted into the center comes out clean or with just a few moist crumbs (not wet batter). The top should be golden brown. Let the bread cool in the pan for 10 minutes, then turn it out onto a wire rack to cool completely before slicing. Cooling it slightly in the pan helps it set and hold together, but turning it out to the rack prevents the bottom from becoming soggy.