Butter Cream Sandwich: Japanese Confection Reimagined

Butter Cream Sandwich Directions

• Prepare Raisins Properly
  Soak 100g raisins in water with 1% salt for 1 hour to clean and plump them. Drain thoroughly and pat dry with paper towels. Place in a container and sprinkle with 1+ tablespoon rum. Cover and refrigerate overnight to allow raisins to fully absorb the flavor.
• Bring Ingredients to Temperature
  Remove 120g unsalted butter from refrigerator and let soften until finger easily makes an indentation. Separate 1 egg white and allow to reach room temperature. Melt 80g white chocolate over a double boiler, then cool until just warm but still fluid.
• Create Perfect Meringue
  In a clean, grease-free bowl, beat egg white with 4g sugar using a hand mixer. Start at medium speed, then increase to high until stiff peaks form. Finish at low speed to refine the texture. The meringue should stand with just slightly bent tips when beaters are lifted.
• Prepare Butter Base
  In a separate bowl, beat softened butter until pale and fluffy, about 3-4 minutes with a hand mixer. The butter should increase noticeably in volume and develop a lighter color. This aeration is crucial for achieving the final silky texture.
• Combine With Precision
  Switch to a rubber spatula and add meringue to whipped butter in five small additions. Completely incorporate each addition before adding the next. This gradual process maintains the air incorporated in both the butter and meringue.
• Add White Chocolate
  Gradually stream in the cooled melted white chocolate while constantly folding with the spatula. Continue folding until the mixture is homogeneous and develops a smooth, silky consistency. The mixture will become slightly thicker.
• Incorporate Raisins
  Roughly chop half the rum-soaked raisins, leaving the remaining half whole. Gently fold both chopped and whole raisins into the buttercream until evenly distributed. The varied texture creates a more interesting mouthfeel.
• Use and Store Properly
  For sandwich cookies, spread between cookies and refrigerate overnight to allow flavors to meld and texture to set. When using as a spread, allow refrigerated buttercream to soften at room temperature and stir before using. Store in refrigerator for up to one week.