In the bowl of an electric stand mixer, fitted with paddle attachment, whip butter on medium-high speed until very pale and fluffy 6 - 8 minutes, frequently scraping down sides and bottom of bowl.: As you whip the unsalted butter , listen for a change in the sound from heavy thumping to a lighter, airy whir, and watch the color shift to a pale, almost ivory hue. The texture should become billowy and soft, with tiny air bubbles visible when you lift the paddle. This aeration is what gives the frosting its light mouthfeel and keeps it from being dense. If you stop too early the butter will remain heavy and the frosting may be greasy, so patience here results in a silkier final texture. A common pitfall is starting with butter that is too cold, which resists whipping, or too warm, which can collapse; aim for room temperature but slightly cool to the touch.
Meanwhile, pulverize freeze dried strawberries in a food processor until finely ground (wait about 10 seconds before opening food processor allowing the powder in the air to settle a bit. There should have 3 1/2 tbsp of the strawberry powder).: When the freeze dried strawberries are pulsed, you will see them transform from brittle shards to a vivid pink powder that smells intensely of strawberry. That aroma hitting your nose is the concentrated fruit oils releasing, and it is the heart of the flavor. Let the dust settle for the seconds recommended so you avoid a pink cloud, and check the grind for a flour like consistency. If bits remain, continue pulsing gently. A mistake people make is over processing while the blades heat slightly, which can warm the powder and reduce aroma, so pulse in short bursts.
Transfer strawberry powder to whipped butter and blend mixture until combine. Stir in heavy cream followed by powdered sugar and whip mixture 4 - 5 minutes longer on medium-high speed, until very pale and fluffy, frequently scraping down sides and bottom of bowl. For best results frost and serve within an hour.: Once the powder hits the whipped butter, you will notice an immediate blushing of color and a fragrant lift in the bowl. Blend on low at first so the fine powder incorporates without puffing into the air. The texture will tighten slightly as the sugar and powder absorb some fat, but the mixture should remain silky. This step is crucial for even color and flavor distribution, because unmixed pockets of powder create specks in the frosting. Avoid adding the powder too quickly, which can cause clumping; instead fold briefly and then increase speed to finish smoothing.
Stir in heavy cream followed by powdered sugar and whip mixture 4 to 5 minutes longer on medium-high speed, until very pale and fluffy, frequently scraping down sides and bottom of bowl: After you add the heavy cream , the bowl will sound a touch thinner and the mixture will loosen, so follow with the powdered sugar in stages. The frosting will grow lighter in color and become almost ribbon like when you lift the paddle. Whipping for the full four to five minutes develops volume and ensures the sugar is fully integrated, removing any graininess. If you whip too briefly the texture may be uneven, and if you over whip for very long you risk incorporating too much air, which can make the frosting fragile. Scrape the bowl frequently so all ingredients are evenly mixed and you do not end up with pockets of dry sugar.
For best results frost and serve within an hour: The finished frosting will have a glossy, slightly satiny surface and will hold peaks when piped. The strawberry aroma will be most pronounced soon after making it, and piping at room temperature ensures smooth edges. If you wait too long before using it may settle slightly and lose some loft, but it can be re whipped briefly to revive texture. A common error is storing the frosted cake in a warm room where the buttercream softens too much, so keep it cool if you need firmer decoration.