Add room temperature butter to a large mixing bowl or the bowl of a stand mixer fitted with a whisk or paddle attachment. Whip the butter for 5 minutes on medium-high speed, scraping down the sides occasionally, until the butter is light, fluffy, and pale in color.
Add one half of the powdered sugar and mix on the lowest speed setting until fully combined. Add remaining powdered sugar and continue to mix on low until incorporated.
Add orange juice, orange zest, vanilla extract, and salt and mix on low until combined.
Slowly drizzle in the heavy cream while mixing on low speed. Scrape the sides of the bowl occasionally to ensure the frosting is well mixed.
Once the heavy cream is added, turn the speed on the mixer to medium and mix for an additional 3 minutes until smooth.
Optional - If you are using a whisk attachment, switch to a paddle attachment and mix the buttercream on low speed for several minutes to remove air bubbles. You can also mix the buttercream by hand with a spatula to smooth it out as well.