Blueberry jam recipe request

[iz22]

I've been given some blueberries to make jam. Usually I would use an equal weight of fruit and sugar, to ensure the jam lasts well, but all of the recipes I have found online use quite a lot less sugar than blueberries. Does anyone have a tried and tested recipe for me please, using equal amounts of blueberries and sugar? Many thanks.

For keeping, I understand it is ok to go down to 1 part fruit to three quarters sugar by weight. I have done this with rhubarb and strawberries for example.