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Preheat oven to 350 degrees. Line a baking sheet with parchment paper and set aside.
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Place the flour, baking powder, baking soda, and salt in the bowl of an electric mixer fitted with the paddle attachment, the bowl of a food processor, or in a large bowl and mix by hand. Sift ground cardamom seeds into mixture; stir to combine. Add butter and mix until crumbly.
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Add ginger, sour cream, 1/2 cup sugar, and 1 egg. Mix, blend, or pulse, just until combined; do not overmix.
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Form 1/3 cup dough into a ball or use a large ice cream scoop, and place dough on prepared baking sheet. Repeat with remaining dough, spacing scones about 2 inches apart.
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In a small bowl, mix together remaining egg with a dash of water. Brush scones with egg mixture and sprinkle evenly with remaining 4 teaspoons sugar. Bake until golden brown, 25 to 30 minutes.