Cold butter is key! Cube the butter, and place the cubes onto a small plate in the freezer for 15 minutes.
Mix the dry ingredients. Add the gluten-free flour, sugar, and salt to a stand mixer with a paddle attachment. Turn the mixer on low speed and blend together the ingredients.
Add the cold butter. Add the cubed butter to the flour mixture and toss to coat. This will create flaky layers. Turn the mixer on low speed and hold down the top with both hands, just until the butter starts to break down. (The paddle attachment may whip some of the flour out of the bowl while trying to break down the cold butter, so holding down the top helps avoid this problem.)
Blend the butter into the flour mixture. After 1-2 minutes, use a spoon to sift through the mixture. You want the butter chunks no bigger than the size of walnuts. Anything larger you can quickly break apart with your hands but make sure to not handle the butter too much. Every piece of butter should be coated in flour
Whisk together the wet ingredients. Remove the sour cream, ice water, and lemon juice from the refrigerator. Add the ingredients to a small bowl measured on a food scale. Everything should weigh 80 grams. Whisk together until smooth, (it's ok if there are a few sour cream chunks)
Add the wet ingredients to the dry mixture. Pour the sour cream mixture into the bowl.
Bring the dough together. Turn the mixer on back to low speed, until the dough begins to form. Form the dough. You do not want to overwork the dough, so as soon as the dough starts to collect around the paddle, turn off the mixer. The dough should be moistened, without visibly dry parts of flour. It should also not be overly wet or sticky. You should be able to squeeze the dough and have it hold together
Scrape down the bowl. Remove any excess dough from the paddle attachment, and scrape down the sides of the bowl with a rubber spatula
Turn the dough out onto a piece of plastic wrap. Pour dough out onto a large piece of plastic wrap
Shape the dough. Use the plastic wrap to help gather the dough in a ball. Take one side of the plastic wrap and fold it over the dough, bunching the pieces together. Repeat on the opposite end, shaping the dough and smoothing it out into a disc.
Chill the dough. Place the disc in the refrigerator for at least 30 minutes.