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Preheat the oven to 350 degrees F. Spray a square 8x8-inch baking dish with nonstick spray.
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Combine the oats, flour, baking soda, and salt in a small mixing bowl. Set to the side.
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Add the peanut butter and brown sugar to the bowl of an electric stand mixer fitted with the paddle attachment. Cream on medium until lighter and fluffy. Add vanilla and beat until combined. Scrape down sides as needed.
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With the mixer on low speed, add in the dry ingredients a little at a time. Pour in the milk and mix until dough forms.
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Press the dough into the prepared dish. Spread apple butter over the top.
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Add the butter, flour, brown sugar, oats, vanilla, and cinnamon to a small mixing bowl. Use your fingers to combine until the butter is evenly distributed.
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Scatter the crumb topping over the top of the apple butter. Slightly press into the apple butter.
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Bake for 25-30 minutes until golden. Let cool completely in pan before cutting into 9-12 squares.