3 cups (420g) high-quality all-purpose gluten-free flour, plus more by the tablespoon if necessary (and extra for dusting)
1½ teaspoons xanthan gum (omit if your blend already contains it)
¼ teaspoon cream of tartar
4 tablespoons (48g) sugar
2½ teaspoons instant (or rapid-rise or breadmaker) yeast
½ teaspoon kosher salt
1 teaspoon apple cider vinegar
1 extra-large egg plus 1 extra-large egg white
1 cup warm milk (low-fat is fine, nonfat is not), about 100 degrees F
4 tablespoons unsalted butter, melted and cooled
½ c (140g) water roux (half the yield of the recipe referred to earlier)*