Preheat the oven to 350 degrees F. Prepare a baking dish with parchment paper. Add together the crust ingredients and mix together until a crumbly dough. Pour 3/4 of the dough into the prepared baking dish. Press down into a bottom crust.
In a saucepan add the 2 sticks of butter and place over medium heat to cook until browned and nutty. Pour the browned butter into a large bowl. Add the brown sugar, cinnamon, nutmeg and salt, whisking everything together.
If using canned peach pie filling skip next two steps.
Pour the drained peaches into a mixing bowl. Use a masher to mash the slices slightly. Drain the peaches again from excess juice and place into a sauce pan. Add the lemon juice and sugar to the saucepan and place over medium heat. Let them cook for 15 minutes stirring every minute or so until the peaches start cooking down and a syrup forms. Remove from heat and add the nutmeg and cinnamon and mix together.
Pour the peaches or filling on top of the brown butter crust. Spread into an even layer. Take the remaining 1/4 of the crumbly dough and lightly crumble on top of the peach layer as the streusel. Bake in the oven for 45 minutes or until the streusel has browned.
Let cool for at least 30 minutes before removing from the baking dish and cutting into 9 squares. Enjoy!