Preheat oven to 375°F. Grease and line two 7.75 x 3.75-inch loaf pans with parchment.
In a bowl, whisk gf flour, cornstarch, baking powder, baking soda, salt, sugar, psyllium, and nutmeg.
In a separate bowl, whisk the wet ingredients.
Add dry to wet.
Divide batter evenly between pans, filling each pan ⅔ full. Smooth the tops.
Let pans sit 5 minutes.
Bake for 12 minutes at 375°F, then reduce oven to 325°F and continue baking for 40 to 55 minutes.
Loaves are done when a tester comes out with moist crumbs and the internal temperature reads 200 to 203°F.
Cool in pans for 20 minutes, then lift out and cool completely on a rack before glazing.
Mix all glaze ingredients until smooth.
Add additional milk 1 tsp at a time until glaze ribbons off spoon.
Spoon glaze over cooled loaves and let set for 10 to 15 minutes.
