In the bowl of a stand mixer fitted with the paddle attachment, beat butter and custard powder at medium-low speed until creamy, 2 to 3 minutes, stopping to scrape sides of bowl. Beat in bourbon, vanilla, and nutmeg. With mixer on low speed, gradually add confectioners’ sugar alternately with eggnog, beating until well combined and stopping to scrape sides of bowl. Increase mixer speed to medium, and beat for 1 minute. Use immediately.
Notes
*We used Bird’s Custard Powder, available at select grocery stores and amazon.com.