I can’t remember where I saw this, but it sounded so good I immediately got my recipe notebook and converted it and made the next morning for breakfast.  It was amazing.  You do need to plan ahead a little as it does take a good bit of cooking time.  But, it was worth the wait, moist and delicious with a crispy sweet top.  It says breakfast cake, I think because it is reminiscent of coffee cake, but this cake would be great any time.

Preheat oven to 350 degrees.  Grease a 9-inch square pan.
Serves 6-9 (depending on size of slice you serve)
1/2 cup butter, softened
zest from 1 lemon
3/4 cup + 2 Tablespoons + 1 Tablespoon  sugar (I used cane sugar)
1 egg, room temperature
1 teaspoon vanilla
2 cup GF White Flour – DIVIDED use
1/2 teaspoon xanthan gum
2 teaspoons baking powder
1 teaspoon salt
1/2 cup buttermilk OR plain kefir OR sour milk
2 cups blueberries (The original recipe called for fresh, I used frozen and they worked great, they did “bleed” a little but you couldn’t really tell in finished cake.)
Cream butter, lemon zest and 3/4 cup + 2 Tablespoons sugar until light and fluffy.  Add eggs and vanilla, beat again until light and fluffy.
In a separate bowl whisk 1 3/4 cups flour, xanthan gum, baking powder and salt together.
If using fresh blueberries, take the 1/4 cup flour and toss the blueberries with it.  If using frozen wait until right before you fold into batter otherwise the berries will be melting and make a gummy mess.
Add the flour alternately with the buttermilk.  (I did about three add-ins of each) Once combined well, fold in the floured blueberries.  Spread batter, it’s a bit thick, into the prepared pan.  Sprinkle with remaining 1 Tablespoon of sugar.  Bake 35-35 minutes, it may take longer.  Check it after cooking 35 minutes with a toothpick and then cook in 5-10 minute increments until done. 
 Let cool 15 minutes before serving.  I’ll be honest, I didn’t wait.  My kids were chomping at the bit with hunger by the time it was done.  I did wait about 8 minutes.  It’s better to wait if possible so your cake doesn’t fall apart.  I waited the 8 minutes and it held together pretty well.