baratter

To churn — almost always about making butter from cream in a baratte (butter churn), a term that survives from traditional dairy-farming vocabulary into modern artisanal cheese-making.

• La fermière baratte la crème pour faire du beurre. — The farmer churns the cream to make butter.
• On barattait le lait à la main autrefois. — Milk used to be churned by hand in the old days.
• Ce beurre est baratté selon des méthodes traditionnelles. — This butter is churned using traditional methods.

Baratter is specific to the physical churning process for butter — French doesn't extend it metaphorically the way English sometimes uses 'churn' (e.g., for churning out content).