In microwave-safe bowl heat butter until completely melted; set aside.
In a separate bowl, warm 1/2 cup milk to 110-115°F. Whisk in yeast and let sit 5 minutes.
In a large mixing bowl, add sugar, butter and milk-yeast mixture; beat until light and fluffy. Add in eggs, one at a time, mixing after each egg is added. Add in lemon juice and remaining milk (at 70°F).
In a separate bowl whisk together flour, xanthan gum, and salt. Add to mixing bowl, 1 cup at a time, and mix until just combined.
Pour batter into prepared bundt pan. Cover and place in warm area to rise, about 30 minutes.
Preheat oven to 325°F.
Uncover and bake for 45-60 minutes, until golden brown and toothpick come out clean when inserted into cake.
Remove from oven and let cool for 5 minutes in pan. Invert pan on cooling rack to remove cake from pan. Let cool for 1 hour.
Meanwhile, whisk together powdered sugar, salt, milk and lemon juice. Add more/less milk to achieve desired thickness. Once cake is cooled, top with glaze.