In the bowl of a stand mixer, gently mix together the yeast and 1/2 tsp sugar. Slowly add in the warm water (so it doesn't splash the yeast up the bowl). Let it sit for at least 15-20 minutes until the mixture is completely foamy.

While the yeast is blooming, sift together the gluten free flour, cornstarch, xanthan gum, salt and baking powder in a separate bowl.

Butter a 9x5 inch loaf pan with about two Tbsp butter. Make sure to grease the sides all the way to the top of the pan.

When the yeast is ready, add the warm milk, canola oil, 2 Tbsp butter, eggs, white vinegar and the remaining sugar to the bowl. Mix on low until ingredients are combined. The butter will still be lumpy since it's not melted.

Add the dry ingredients and mix on low until completely combined. Set the mixer to a medium speed (I use 6 on my Kitchen Aid) and mix for 5 minutes. Scrape the bowl down as necessary - I didn't need to scrape mine but all mixers are a little different.

Transfer dough (it will be the consistency of a quick bread) to the prepared loaf pan. Smooth out the top with wet hands. Lightly cover with plastic wrap and set the bread in a warm place to rise for 1 hour and 15 minutes. Leave a tiny air vent on one corner of the pan. The dough will rise to the top of the pan.

When the bread is done rising, preheat the oven to 375 degrees. Very gently move the bread to the oven and bake for 20 minutes. After the 20 minutes, reduce the oven temperature to 350 degrees and loosely cover the bread with aluminum foil so it doesn't get overly brown. Bake for an additional 20 minutes.

Cool the bread in the pan for about 10 minutes then remove from the pan and cool completely on a wire rack.

Store bread in an airtight container or cut into slices and freeze.