Start by making the crumb topping. In a medium bowl, stir together ¼ cup brown sugar, ¼ cup flour, 2 tablespoons melted butter, 1 teaspoon cinnamon, and a pinch of salt. It should be a relatively crumbly texture. Set aside.
Preheat the oven to 350F. Grease and line an 8x8-inch baking pan with parchment paper (optional but recommend; grease well if not using parchment paper.) Set aside.
Start by creaming together the softened butter and granulated sugar with a hand mixer or stand mixer on medium speed until light and fluffy, about a minute.
Add in the sour cream, egg, and egg white, mixing until just combined. You'll notice that the butter clumps up and the batter no longer appears super smooth; this is okay.
Stir in the dry ingredients: all-purpose flour, baking powder, baking soda, salt. Stir until just combined.
Transfer half of the batter to the greased/lined pan, smoothing it out as able. It's a relatively thick batter and it's okay if it doesn't spread perfectly. Top with an ample layer of cinnamon.
Top with the remaining batter, spreading out across the top of the cinnamon layer. Again, it's okay if it doesn't spread perfectly to the edges.
Top with the peach slices, then cover with the chopped pecans and brown sugar crumb topping.
Bake at 350F for 40-45 minutes, or until the cake is puffed up in the center and the edges are pulling away from the pan. The center should bounce back slightly when touched gently.
Let cool in the pan for 5 minutes before turning out onto a cooling rack. Use a knife to separate the edges of the cake from the pan, as needed.
In a small bowl, whisk together the powdered sugar and 2 tablespoons of milk until smooth. It should be easy to drizzle. Add extra milk 1 tablespoon at a time, as needed.
Drizzle the cooled coffee cake with the powdered sugar glaze. Slice and enjoy!
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Notes
Peach: One large peach or two small peaches. The peach should be ripe and soft to the touch. I leave the skin on. I have not tested this recipe with canned or frozen peaches, but they should work if drained/thawed. Pat dry before adding to the coffee cake.
Sour cream: Do not use reduced-fat/fat-free sour cream as it can affect the coffee cake texture.
To make muffins: Makes 12 standard muffins. Distribute the coffee cake batter across muffin liners and top each muffin with a peach slice or two. Bake at 350F for 20-22 minutes. Note that these are flat muffins; I plan to create a more "perfect" rounded coffee cake muffin in the future and will update this note when I do.
Storage notes: Keeps well at room temperature for 2-3 days in a closed container. To extend its shelf-life, I recommend refrigerating after the first 2 days. Freezes well for up to 3 months. Let thaw on the counter or in the fridge.
I use a kitchen scale for all of my Lynn's Desserts recipes. Select "metric" on the recipe card to see gram measurements.