Preheat oven to 350° F.
Spray a 9×13 glass baking pan with cooking spray.
In a large bowl add the gluten-free flour, xanthan gum (leave out if your flour already has it), salt, sugar, baking powder, milk, eggs, and vanilla and mix until fully combined.
Once combined stir in the melted butter.
The cake batter will be very thick and sticky. Pour into the prepared 9×13 baking pan.
In a large bowl, cream butter, brown sugar, gluten-free flour and cinnamon together with a mixer.
Drop heaping tablespoonfuls of the butter mixture into the cake batter.
Use a knife to swirl the butter mixture through the cake.
Bake at 350 degrees for 35-40 minutes. Use a toothpick to check and see if the center is done.
In a medium bowl, whisk the powdered sugar, milk and pure vanilla extract together.
Pour over the warm cake.
Store in an air-tight container.
(Courtesy of www.mamaknowsglutenfree.com)
3 cups *gluten-free flour
1 1/2 teaspoons xanthan gum
1/4 teaspoon salt
1 cup sugar
4 teaspoons gluten-free baking powder
1 1/2 cups milk (For dairy-free use cashew milk, almond milk, or coconut milk.)
2 teaspoons pure vanilla extract
1/2 cup unsalted butter melted (For dairy-free use margarine.)
1 cup unsalted butter softened (For dairy-free use margarine)
1 cup packed brown sugar
2 tablespoons gluten-free flour
1 tablespoon cinnamon
2 cups powdered sugar
5 tablespoons milk (dairy-free use cashew, almond or coconut milk)
1 teaspoon vanilla