I'm taking some liberties with the word "fudge" here. To be honest, I tried filling these thumbprint cookies with honest-to-goodness-candy-thermometer-required-made-on-the-stovetop fudge. It was a lot of work.  I did it multiple times and each time the fudge pooled nicely in the cookies and made a smooth little puddle of peanut butter and they really didn't taste bad.