Preheat the oven to 350 degrees. Grease and flour a 10 or 12 cup Bundt pan.
In a large mixing bowl, use an electric mixer to cream together the butter and sugar until well combined.
Add the eggs, one at a time, and beat until combined. Then add the vanilla and sour cream and beat until completely incorporated.
In a medium mixing bowl, whisk together the gluten free flour, baking powder, baking soda, and salt.
Add 1/3 of the flour mixture to the batter, and with the mixer on low, beat until just combined. Continue to add 1/3 of the flour and mixing on low until all the flour has been incorporated.
Use a rubber spatula to scrape down the sides of the bowl and make sure the batter is completely combined.
In a small mixing bowl, add the brown sugar, gluten free flour, cinnamon, salt, and cold butter pieces. Use a fork, or your fingers, to press the streusel ingredients together until it forms crumbs.
Sprinkle 1/2 cup of the streusel in the bottom of the Bundt pan. Spoon half the batter over the streusel and spread evenly with a knife. Sprinkle the rest of the streusel on top of the batter. Then spoon the remaining batter over the streusel and spread it out.
Bake for 50 to 55 minutes, until a wooden pick inserted in the middle comes out clean.
Allow the cake to cool on a wire rack for at least 30 minutes. Then invert the cake onto a wire rack to cool completely.
Whisk the powdered sugar and milk together to form the glaze. Stir in additional powdered sugar or milk to achieve the desired consistency. Use a spoon to drizzle the glaze over the cake.
Recipe adapted from Barefoot Contessa
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