Preheat oven to 375 degrees Fahrenheit. Lightly grease a 9x13 pan.
Place peaches into the prepared pan. Toss with cornstarch, cinnamon, and nutmeg.
In a medium sized mixing bowl, stir together flour, sugar, baking powder, and salt until well mixed. Sprinkle over the top of the peaches in an even layer. Sprinkle brown sugar on top.
Use a cheese grater to grate the butter. Sprinkle grated butter over the top of the cake mix layer.
Bake in the preheated 375 degree oven for 35 to 40 minutes, until golden.
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Notes
If using frozen peaches, let thaw at room temperature for about 30 minutes prior to using them in the recipe. To use canned peaches, use 45 to 60 ounces of canned peaches packed in water, not syrup. Drain well. Pro Tip: The nature of dump cakes make it difficult to spread your flour mixture evenly. High spots may not mix with liquids and remain raw. If you notice raw spots while baking, simply use a spoon to flatten out the high spot out so it can absorb some liquids.