In the bowl of a stand mixer or large bowl if using an electric mixer, beat 1 cup unsalted butter, softened, for 30-40 seconds, until creamy and smooth using an electric mixer or stand mixer with the paddle attachment.
Gradually add 2 cups powdered sugar, ½ cup at a time, and beat on low speed until well combined. Scrape down the sides of the bowl as needed.
Add 7 ounces white chocolate, melted, ½ teaspoon vanilla extract and a pinch of salt to the butter mixture. Beat at medium-low speed until the ingredients are fully incorporated. If needed for a spreadable consistency, add heavy or whipping cream, one tablespoon at a time, while continuing to beat the mixture.
Once all the ingredients are well combined and the desired consistency is achieved, increase the mixer speed to medium-high and beat the buttercream to achieve a smooth texture for 2-3 minutes until it becomes light and fluffy. Taste the buttercream and adjust the sweetness or flavor if desired. You can add more powdered sugar for a sweeter taste or additional vanilla extract for more flavor.
If you're not using it immediately, store it in an airtight container in the refrigerator. Allow it to come to room temperature before using and give it a quick whisk to restore its fluffy texture.