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Preheat oven to 350°F.
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In large bowl, combine 2 1/4 cups flour, sugar, baking powder, baking soda, and salt and mix well.
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Add eggs, buttermilk, vegetable oil, and lemonade concentrate and beat well combined.
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Stir in blueberries.
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In medium bowl, combine butter, brown sugar, 2/3 cup flour, and oatmeal and mix until crumbly.
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Spray a 12-cup bundt pan with non-stick baking spray.
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Pour half of batter into pan and sprinkle with half of streusel mixture.
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Repeat layers, ending with struesel mixture.
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Bake at 350°F for 45-50 minutes, or until toothpick into center comes out clean,cake is brown, and pulls away from edges of pan.
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Let cool in pan for 10 minutes, then invert onto serving plate.
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Serve warm, dusted with powdered sugar.