Gold Time: Butter Street 2

15 sour cream and 2 cows in 4:30.

Since you start off with 1 cow, this isn't too hard. Start processing milk into sour cream, butter, and cheese. Sell the cheese (and a few bears) until you can afford another cow. Then, sell cheese until you can afford to upgrade your Separator.

It's easy to meet your goal in 3:45