Preheat oven to 350° Fahrenheit (176° Celsius).
In a large mixing bowl, whisk together the dry ingredients: flour, sugar, baking powder, salt, cinnamon, and nutmeg.
In a smaller mixing bowl, combine wet ingredients: sourdough discard, milk, vanilla extract, butter, and egg.
Pour wet ingredients into dry ingredients and stir until just moistened.
Pour batter into a lightly greased 9-inch by 5-inch baking pan.
Bake at for 50 minutes to 55 minutes. Internal temperature should reach at least 195° Fahrenheit (90° Celsius).
Let cool in pan on wire cooling rack for 15 minutes.
Use a knife to loosen bread from pan and turn out onto wire cooling rack to finish cooling.
While bread cools, stir together powdered sugar and milk to form a glaze. After the bread has finished cooling, drizzle glaze over the top.