Place the brown sugar, flour, butter, and cinnamon in a bowl and using a pastry cutter, cut in the butter then switch to your hands and squeeze together to form clumps of topping.
1/2 Cup Brown Sugar, 1/2 Cup Flour, 1/2 teaspoon Cinnamon, 4 Tablespoons Butter
To Bake
Bake at 400 for 15 minutes, remove from the oven and add the remaining peaches on top.
Bake an additional 10-12 minutes, remove from the oven again and add the topping in little clumps all over the pie, returning the pie to the oven for another 20 minutes, covering the crust with foil if needed.
Allow to cool on the counter then put in the fridge for 3 hours to set.