I've added it to my shopping list, thanks so much for the tip!Add about 3/4 cup of powdered milk when you plant new ones. As you water it releases extra calcium.
PS you can also mix some up and spray the base of the plant throughout the growing season.
Here's a link
https://homeguides.sfgate.com/use-powdered-milk-end-blossom-rot-71917.html#:~:text=Once a tomato is affected,help prevent blossom-end rot.