In a medium bowl, combine the flour, brown sugar, cinnamon, and salt. 130 g soft brown sugar, 125 g all-purpose flour, 1 1/2 tsp ground cinnamon, Pinch salt
Add the cold, cubed butter and use a pastry cutter or your fingers to rub the butter into the flour mixture until it resembles coarse crumbs, in varying sizes. Refrigerate the streusel while you prepare the cake batter. 100 g unsalted butter
Cake batter
Line an 8x8-inch square baking pan with parchment paper, leaving an overhang on two sides for easy removal. Preheat the oven to 350°F (180°C).
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside. 190 g all-purpose flour, 1 1/2 tsp baking powder, 1/2 tsp baking soda, 1/4 tsp salt
In a large bowl using an electric mixer, cream together the softened butter, granulated sugar, oil, and vanilla until light and fluffy, around 3-4 minutes. Scrape down the sides of the bowl as needed. 113 g unsalted butter, 1 tbsp oil, 150 g granulated sugar, 1 tsp vanilla paste
Beat in the eggs one at a time, mixing well after each addition. Mix in the Greek yogurt until combined. 2 large eggs, 120 g Greek yogurt
Add half the dry ingredients and fold gently with a spatula. Add the milk, fold to combine, then add the remaining dry ingredients and fold until just combined. Do not overmix. Gently fold in the diced peaches. The batter will be thick. 60 g milk, 360 g diced peaches
Assemble and bake
Spread half the batter into the prepared pan. Sprinkle half the chilled streusel evenly over the batter.
Dollop the remaining batter on top in spoonfuls and gently spread to cover the streusel layer. It's OK if it's not perfectly even.
Sprinkle the remaining streusel evenly over the top.
Bake for 50-60 minutes until the cake is golden and a toothpick inserted into the center comes out clean. If the top is browning too quickly, loosely tent it with foil for the last 10-15 minutes.
Let the cake cool in the pan for 15 minutes, then use the parchment overhang to lift it out onto a wire rack to cool completely.
Vanilla glaze
Whisk together the powdered sugar, vanilla, and milk until smooth and pourable. Add the milk a little at a time to reach your desired consistency. 60 g powdered sugar, 1/2-1 Tbsp milk, 1/4 tsp vanilla paste
Drizzle the glaze over the cooled cake.
Notes
You can also make it with canned or frozen peaches, though they will have less texture than fresh. If using canned, drain them well and pat them dry to avoid excess moisture. For frozen peaches, thaw them completely and blot any liquid before layering adding them to the batter.Both US customary and metric measurements are provided. Use the toggle to switch between the two.