Whisk together gluten free flour, poppy seeds, baking powder, baking soda, and salt. Set aside.

Measure sugar and orange zest together in bowl of stand mixer (or use a regular bowl if you have a hand mixer) and rub together with your fingers for a minute or so until the sugar becomes a yellow/orange color and is fragrant.

Add butter to sugar/zest and mix using medium speed until mixture is pale yellow/orange and fluffy.

Add vanilla and eggs one at a time, beating after each addition. 

Add flour mixture, sour cream, milk, and freshly squeezed orange juice. Mix on medium-low just until creamy and any lumps are gone.

Let the mixture sit while the oven preheats to 350. 

Line a loaf pan with parchment or grease well with butter, oil, or cooking spray.

When the oven is preheated, spread batter into prepared pan and bake for 45-55 minutes until the loaf is golden brown and a toothpick inserted in the center comes out clean.

Allow the loaf to cool on a rack while you prepare the glaze.

FOR POWDERED SUGAR GLAZE: whisk together powdered sugar and freshly squeezed orange juice to make desired consistency. Pipe or drizzle onto the loaf when it has completely cooled.

Store leftover bread in an airtight container or bread bag in the fridge for 5-7 days. You can also freeze.