Whole Milk and Butter (Best Option)
3/4 cup whole milk + 1/4 cup melted unsalted butter per 1 cup heavy creamHeavy cream is about 36-40% fat, which contributes to the creamy texture and richness of the mashed potato topping in Shepherd's Pie. Combining whole milk (3.25% fat) with melted butter (about 80% fat) raises the overall fat content to approximate that of heavy cream, ensuring the potatoes remain creamy and do not become watery.
To ensure success, melt the butter and whisk it thoroughly into the whole milk before adding to the potatoes. Add gradually to avoid over-thinning the mash. Use unsalted butter to control seasoning.
Compared to using pure heavy cream, this substitute yields a very similar texture and mouthfeel, with only a slight difference in flavor that is generally imperceptible in the context of the dish's robust savory components.