Before you begin: Make sure your butter and cream cheese are both at room temperature and feel the same temperature to the touch. If one is cold, you will end up with lumpy frosting. If they feel cold, microwave them in 10-second bursts until they match.
Make the Frosting
In the bowl of a stand mixer with the paddle attachment, add the room-temperature cream cheese and mix on low speed until smooth. You can also use a large bowl and an electric hand mixer.
With the mixer on low to medium speed, add the butter in chunks and mix until incorporated.
Slowly pour in the granulated sugar while the mixer is running on low.
Add the salt and vanilla and mix to combine.
Scrape the sides and bottom of the bowl well, then mix on medium-high speed for 30 seconds to 1 minute until all the butter chunks are smoothed out and the sugar is dissolved.
Use the frosting right away to frost a cake, cupcakes, or cinnamon rolls.
Video
Notes
Use full-fat block cream cheese, not spreadable tub cream cheese. Tub cream cheese has too much water and will make the frosting too soft to pipe.
The butter and cream cheese must be at the exact same temperature before mixing. If either is cold, microwave in 10-second increments until they match.
Scrape the sides and bottom of the bowl thoroughly before the final mix. Cream cheese hides under the paddle and will leave streaks if not scraped.
Do not over-mix once the frosting looks smooth and fluffy. Thirty seconds to one minute on medium-high at the end is all you need.
This frosting can be left at room temperature for up to 4 hours. Refrigerate for up to 5 days in an airtight container.
Freeze for up to 3 months. Bring fully to room temperature and rewhip briefly before using.
This is not a crusting frosting and is not recommended under fondant.
Flavor variations: substitute vanilla with almond extract, lemon zest, or orange zest. For a chocolate version, add ¼ cup of sifted cocoa powder with the sugar, or more if you want more chocolate flavor.
Yield: About 4 cups of frosting. Nutrition is calculated per 1 cup.