Runny lemon curd! Help!

I can attest to the re-heat method. I had initially followed the timing in the recipe, which was ridiculously short in retrospect-5 minutes on a double boiler - and hoped the curd would firm up after the butter addition and cool down. That didn't happen so I put it back on a double boiler and stirred for another 10-12 minutes and it came together like a charm.

I used JustSomeCooks' recommendation. I only had powdered gelatin, so I bloomed it and added it to the curd and gently heated it. It worked perfectly, and, as mine was orange curd, which is harder to thicken than lemon curd (due to less acidity), I was delighted. I had already added the butter, so I was cautious about heating it gently so as not to split the butter. I had made 6 cups, so finding a solution was terrific. Thank you, JustSomeCook!

I had a similar problem. It was my first time making curd and the recipe said to cook it 5 to 7 minutes in a double boiler over med-high heat. After 9 minutes it was still runny but I was afraid to cook it any longer and hoped it would set as it cooled. It didn't. Before dumping it and starting over, I decided to try cooking it again. The butter had already been added so I wasn't sure how it would go, but after about 15 minutes of cooking, it started to thicken up. The taste and consistency seem fine, at least for my purposes. Worth a shot.

Have to agree with china millman - it sounds like you didn't cook it long enough. Assuming you used a recipe with the right ratios, the egg yolks will eventually get there (even if it seems to be taking forever). I'd re-do it.

My concern is that if the lemon curd is too runny, you may not have heated it enough to sufficiently cook the eggs. If you used pasteurized eggs, it's probably fine and I would go with JustSomeCook's suggestion, but if you didn't, I wouldn't risk it. Buy some good jam and use that instead, or make another batch.

Your best bet is to throw some bloomed gelatin in there and heat it just enough to melt it in. Maybe a sheet per quart, sight unseen.