How to Make It
Preheat oven to 350°F. Coat a 12- to 15-cup Bundt pan with baking spray.
Beat granulated sugar and butter with a stand mixer fitted with a paddle attachment on medium-high speed until pale and fluffy, 2 to 3 minutes, stopping to scrape down sides of bowl as needed. Add eggs 1 at a time, beating until just combined after each addition. Add vanilla, beating until just combined.
Whisk together flour, baking powder, salt, nutmeg, and baking soda in a medium bowl. With mixer on low speed, gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating until just combined after each addition. Spoon batter into prepared pan; gently tap on counter 3 to 5 times to release air bubbles.
Bake in preheated oven until a wooden pick inserted in center of cake comes out clean, about 50 minutes. Let cool in pan on a wire rack 15 minutes. Invert cake out of pan onto a cutting board or platter, then gently flip cake back over so rough side is facing up. Let cool on wire rack completely, about 1 hour.
Whisk together powdered sugar and water in a medium bowl until smooth. Brush over cooled cake. Slice and serve.