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Preheat the oven to 375 degrees Fahrenheit
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In a bowl mix the flour, baking powder, baking soda, salt and walnuts together, and set aside.
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In a stand mixer, mix together all the wet ingredients on low speed.
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Slowly add in the dry and mix till the batter forms.
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Spoon out the batter into pre-prepped muffin pans and sprinkle with the crumble mixture (cold butter, flour, cinnamon and brown sugar)
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Bake for about 15 minutes or till a toothpick when inserted in a muffin, comes out clean.