Substitution help Needed Please

Yogurt is a good sub.

If... Not I'd... Stupid spell check😉

Put one TBSP. Of lemon juice or vinegar into a measuring cup. Add enough milk or half & half to get to the required total amount of buttermilk needed. Lett it set for about 5 minutes. It will look curdled. You want this. That is what it is supposed to do. Stir it, then proceed with the recipe. So I'd your recipe calls for one cup etc of buttermilk, that is the total amount you should have in the measuring cup. I do this all the time because I don't want a a quart (the least amount available for purchase here.)of buttermilk in my fridge forever. You could also sub out yogurt measure for measure.

I usually do 1 tsp of apple cider vinegar or white wine vinegar with a cup or so of milk (you might want to check my portions here, bc I love sour things). Let sit for a bit and it should curdle just enough to replace the buttermilk! Hope it works out!

I'd be wary about substituting with straight milk, I believe that buttermilk has acid that reacts with the leavening agents ( baking powder/baking soda). You can make a substitute with milk and lemon juice. Use a little less than a cup of milk and add one table spoon of lemon juice ( I think I read you could also use white vinegar but I'd double check that ). If you do go with straight milk, the cake might not rise as much and will have a different texture. Hope that helps :)