Add softened vegan butter to a large mixing bowl and use an electric hand mixer to beat until fluffy — about 1 minute. Add strawberry purée and beat again until fully incorporated, scraping down the sides as needed.
Begin adding sifted powdered sugar 1/4 cup (28 g) at a time (sifting reduces clumps). Mix on low speed until each 1/4 cup is well incorporated and thick yet spreadable. We found that 3 ½ cups (392 g) was the sweet spot (literally)!
Spread frosting on a fully cooled strawberry, vanilla, or chocolate cake and enjoy! Use immediately or store frosting in the refrigerator up to 5 days or in the freezer up to 1 month.
Video
Notes
*Recipe as written makes ~2 cups of frosting.
*Nutrition information is a rough estimate calculated with the lesser amount of powdered sugar.