What You Need to Know
When butter is kept below 0 °C, its fat crystals remain solid during mixing, creating distinct layers that melt during baking and produce a light, flaky structure. The 1:1 butter‑to‑flour ratio balances moisture and fat, while minimal mixing preserves the shortbread’s characteristic crumb. Fine confectioners’ sugar provides a fine crystalline structure that aids in crumb cohesion, and the optional whole‑milk powder adds protein to help set the crumb without excessive gluten formation.
The Science
Primary Reaction
Maillard browning and fat crystallization