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1
Preheat oven to 350u00b0F.
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2
Spray pan liberally with nonstick cooking spray. Set aside.
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3
Place butter, sugar, and vanilla into mixing bowl. Use mixer to cream ingredients together on medium-high speed until smooth, 1-2 minutes. Add eggs, sour cream, and buttermilk, and continue beating until mixture is light and fluffy, about 1 minute.
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4
Sift gluten-free flour, baking powder, baking soda, and salt into bowl. Mix on low speed, scraping down sides of bowl with rubber spatula as needed, until a smooth, thick batter forms.
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5
Scrape batter into pan with rubber spatula and smooth it into an even layer.
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6
Place gluten-free flour, brown sugar, granulated sugar, cinnamon, and salt in a large mixing bowl. Stir with a fork to combine. Drizzle melted butter into bowl and mix with fork until mixture forms large crumbs. Sprinkle crumble evenly over cake batter.
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7
Bake on middle rack of oven until topping is golden and toothpick inserted in center comes out clean, 35-45 minutes.
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8
Check to see that coffee cake is done. Remove from oven or add time as needed.
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9
Allow cakes to cool in pans for 15-20 minutes before serving. To store, cover tightly with aluminum foil or store in an airtight container and keep at room temperature for 1-2 days, refrigerate for up to 1 week, or freeze for up to 2-3 months.
