Melt the butter in a microwave-safe bowl for 20-30 seconds. Brush a 9” springform pan with some melted butter, line with parchment paper, and brush the parchment paper with butter as well. Set the pan aside and allow the rest of the melted butter to cool.
Preheat oven to 350°F.
To make the streusel, combine flour, sugar, and cinnamon in a small bowl, mix together thoroughly with a whisk. Cut the cold butter into small cubes and add to the dry mixture. Use a pastry blender to cut the butter into the dry mixture until coarse crumbs form. Cover and refrigerate until ready to use.
In another small bowl, measure out flour, sugar, salt, and baking powder, mix together thoroughly with a whisk and set aside.
Add softened cream cheese, egg, the cool butter, and vanilla extract to a medium mixing bowl and cream until smooth.
Fold the dry ingredients into the wet ingredients with a spatula until just combined. Fold in the diced peach.
Pour batter into prepared pan. Use the spatula to distribute the batter evenly and create a flat surface.
Sprinkle the cold streusel over the top evenly.
Bake for 40 minutes until an inserted toothpick comes out clean.
Let cool on a wire rack until cool enough to handle before unmolding the cake.