Hello G_Reynolds38. To create a direct substitute for 1 cup of heavy cream using milk and butter, the ideal ratio is 3/4 cup (180 ml) of whole milk combined with 1/4 cup (57 grams, or 4 tablespoons) of melted unsalted butter.
To prepare the mixture, melt the butter gently in a small saucepan or microwave-safe bowl and allow it to cool slightly so it is warm rather than piping hot. Gradually whisk the milk into the melted butter until the liquids combine thoroughly. Using whole milk is recommended here as its fat content provides the closest body and texture, though 2% milk can work in a pinch.
When using this combination in a multicooker vegetable soup, timing is very important. You should always stir in the milk and butter mixture at the very end of the cooking cycle, after high-pressure cooking or slow cooking has concluded. Set your multicooker to the Keep Warm function, pour in the dairy mixture, and gently stir until warmed through. Subjecting milk to high pressure or rapid boiling can cause the dairy proteins to curdle or separate.
Finally, keep in mind that while milk and butter replicate the butterfat content and rich mouthfeel of heavy cream, milk contains more water and less natural viscosity. If you find you need additional thickness for your vegetable soup, you can blend a portion of the cooked vegetables into a puree before stirring them back in, or whisk 1 tablespoon of flour or cornstarch into the cold milk before combining it with the warm butter.
