I’m hoping to make a few Peach Galettes and have a litre of buttermilk on hand and hope to use it in place of the water/cream and cider vinegar in the cream cheese pastry.  Will it be acidic enough to replace the vinegar?  I’m sure it should be fine in place of the water/cream.

The answer is…
It depends. Most modern buttermilk is made with low fat milk. I think the acid balance should be fine but you would be a little low on fat for the recipe. You could add some extra butter to compensate.

I’m not too worried about the fat since Rose uses cream/water interchangably for the recipe.  It is 3.25% so a bit higher in fat content.

It should work just fine.  It may not be as tender as with the vinegar, so you may want to be extra careful to avoid overhandling and consider using (or making) pastry flour. 

Please let us know how it works out!

You can also freeze leftover buttermilk (it will separate) and it will still be good for marinating chicken.

Well, I made it with buttermilk and seemed to work ok.  The galettes are in the freezer for future desserts —will let you know when eaten and baked.