So here is the recipe I used.....http://www.marthastewart.com/342396/yellow-butter-cake
The only thing I did different was put the milk in all at one time and before the flour. Well when I did that the milk curdled (it was brand new, just bought it yesterday morning and used it yesterday). When I was baking the cupcakes the middles fell instead of raising.
Any suggestions on why this might have happened. I have no clue.
Usually cupcakes sink when 1. the oven temperature isn't hot enough or 2. they didn't bake long enough. I don't know if the milk actually curdled or not. Sometimes when adding in milk with a butter mixture it gets the look of being curdled without actually being so. It's usually best to add flour to the batter first before adding the milk as it blends better.
The oven temp was set to 350 and the baked for 20 mins but i thought it was weird that was how they baked. The cupcakes never rose.
Your oven could be off. Also, if you add cold ingredients, they will not emulsify and will look curdled. But they would still bake in most cases.
I didn't look at the recipe, but if you measured correctly, it is probably your oven temp. Improper method would usually affect the crumb, but they would bake somewhat ok.
If you didn't whisk your dry ingredients, the leavener may not have distributed evenly.
Just some ideas.