How to Make It
Preheat oven to 300°F. Beat butter with a stand mixer fitted with paddle attachment on medium speed until creamy, 2 to 3 minutes. Gradually add granulated sugar, beating at medium speed until light and fluffy, 3 to 5 minutes. Add eggs, 1 at a time, beating just until yolk disappears.
Stir together flour and salt in a medium bowl. Add flour mixture to butter mixture alternately with 3/4 cup of the milk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in 1 tablespoon of the vanilla. Gently fold in sprinkles.
Pour into a greased (with shortening) and floured 14 to 16 cup Bundt pan. Bake in preheated oven until a long wooden pick inserted in center comes out clean, 1 hour and 35 minutes to 1 hour and 45 minutes. Cool in pan on a wire rack 10 to 15 minutes. Remove from pan, and cool completely on a wire rack, about 30 minutes.
Stir together powdered sugar and remaining 3 to 4 tablespoons milk, adding last tablespoon, 1 teaspoon at a time, in a small bowl until desired consistency is reached. Stir in remaining 1 teaspoon vanilla extract. Spoon glaze over cooled cake, and immediately sprinkle with sprinkles.