Preheat the oven to 350°F (175°C). Grease and line an 8×8 inch pan with parchment paper.

Make the crumb topping: In a small bowl, mix flour, brown sugar, and cinnamon. Cut in the cold butter until crumbly. Refrigerate until ready to use.

Mix the dry ingredients: In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.

Cream the butter and sugar: In a large bowl, beat softened butter with granulated sugar until light and fluffy.

Add eggs and flavoring: Mix in eggs one at a time, followed by vanilla extract.

Combine wet and dry: Add the dry ingredients to the butter mixture, alternating with sour cream or yogurt. Mix until just combined — don’t overmix.

Fold in peaches: Gently fold the diced peaches into the batter.

Assemble the cake: Pour the batter into the prepared pan and smooth the top. Sprinkle crumb topping evenly over the batter.

Bake: Bake for 45–50 minutes, or until a toothpick inserted in the center comes out clean.

Cool & serve: Let cool in the pan before slicing. Enjoy warm or at room temperature.