I don't think you can make a Beef Wellington without the obligatory mushrooms, it essentially becomes something else.
The whole concept behind beef wellington is to keep the meat juices in by being surrounded by pastry
but there's no reason why you shouldn't omit the mushrooms for something else.
I really can't think of any other food substance that would replicate the flavour of mushrooms without being mushrooms other than truffle.
I would try something like a pork/onion sausage meat stuffing and being the time of year it is, perhaps with chestnuts as a possible alternative, either surrounding the beef or inside it.
cooking.stackexchange.com/users/14539/spiceyokooko
I hate mushrooms too.
The only time I ever made wellington, I simply put a mixture of onions and bacon and cheese in place of the mushroom layer.
I first sprinkled parmesan cheese.
Then I put a layer of finely chopped sauteed onions and then crumpled cooked bacon.
It was fantastic and everyone there said it was the 'best thing they ever ate'.
I realize this isn't really 'wellington' anymore.
But let's face it.
The only real reason anyone wants to eat it is because it's beef and puffed pastry!
That's what's most important I think :)
cooking.stackexchange.com/users/18510/Amanda Connelly
Two years later, the chestnut idea worked swimmingly :D
I followed the recipe I linked in the question, with the following changes: Obviously
, I replaced one pound of mushrooms with one pound of chestnuts.
In hindsight, that was probably a bit too much, as a pound of mushrooms would have cooked down significantly more, but we didn't mind.
In step 3, I omitted the horseradish, as I don't like it.
I'm only reporting that for accuracy :)
I replaced step 4 entirely with the following:
Chop all chestnuts in half, being careful as they have a tendency to fly apart.
Boil the halves in a saucepan of water for 7 minutes.
Drain and let cool, then peel -- this should now be a much easier task.
Chop chestnut meats finely.
I should note that I accidentally boiled them too long, and they got a bit crumbly while I was peeling them.
That didn't matter, because I was going to chop them.
However, in the future I might try using a food processor to chop them, because I ended up with an uneven chop and the larger pieces stood out from the eventual mixture, making it harder to eat.
In step 5, I had to add more butter, as the chestnuts basically absorbed the entire amount of butter called for without actually sauteeing in it.
Not that I minded :) I sauteed the chestnuts until soft, then added the shallots and thyme and proceeded as usual.
I omitted the foie gras, again, added only for accuracy.
Kenji mentioned in the comments that it's not needed if you don't like it or can't find it, so I omitted to make the whole thing simpler.
The dish turned out utterly delicious :D
I don't usually buy beef tenderloin, finding it usually lacking in flavor; since the goal of the dish was to add more interesting flavor and texture back, I definitely feel this was a success.
I realized during the rolling step that I hadn't bought the exact right cut, so it kind of fell apart a bit during serving, but despite all the hard work and mistakes I'd definitely make this again.
cooking.stackexchange.com/users/6317/Yamikuronue
I don't like mushrooms much either, I've made wellingtons with pate mostly, although I've experimented with chopped up brussel sprouts with some success as well.
One thing I would like to try is yellow lentils but haven't had the opportunity.
You could still try mushrooms though if it's the texture your roommate doesn't like rather than the flavor.
If it is texture then try making a rough paste out of mushroom and shallots rather than chopped up pieces.
Or try shitakes instead.
cooking.stackexchange.com/users/19707/GdD
My husband also dislikes mushrooms.
I substituted them for caramelized onions.
Together with the pâté, it turned out quite well, though I agree that substituting the the mushrooms totally changes the character of the dish!
cooking.stackexchange.com/users/23108/Ellin
I have used haggis, and it worked a treat!
The oats soaked up the juices and kept the pastry dry, and it complemented the beef wonderfully.
The only thing I would say is ensure that you only make a thin layer as haggis can have quite a strong taste.
cooking.stackexchange.com/users/23296/Alex Fulton
I find olives tend to keep a similar texture to the mushrooms without bringing their disgusting earthy flavor to the dish :)
cooking.stackexchange.com/users/20804/Jason
I've used both haggis and black pudding as an alternative to duxelle.
Obviously they both change the nature of the dish and is a bit of a faff to prepare (particularly the black pudding) but the combination of flavours is fantastic.
As mentioned above, whether haggis or black pudding, it needs to be quite a thin layer so it doesn't completely overpower the beef.
cooking.stackexchange.com/users/54550/Gordon
I have a mushroom allergy
so i can't make beef wellington with it.
I was thinking about using caramelized onion or garlic and cheese (probably a sharp cheddar or brie) wrapped in bacon or prosciutto.
cooking.stackexchange.com/users/65090/Jacob Burkett
Try sun dried tomatoe pesto on layers of thin slice prosciutto then roll on puff pastry for an Italian style Wellington
cooking.stackexchange.com/users/80083/Lee
I saw a great recipe for Beef Wellington on  Serious Eats  that I'm eager to try. However, my roommate does not eat mushrooms (both because he dislikes the flavor and because he had a bad experience as a child, so "hidden mushrooms" are out too). I worry that omitting them would defeat most of the purpose of the dish. Is there anything that could be used in their place to give a similar flavor?
Mushroom replacement in Beef Wellington
cooking.stackexchange.com
<substitutions><beef><mushrooms>
cooking.stackexchange.com/questions/29305
cooking.stackexchange.com/users/6317/Yamikuronue
Replacing the mushrooms with chestnuts and/or pork/onion sausage meat stuffing can work well, or you can use caramelised onions, possibly with bacon and cheese. Haggis and black pudding, olives or sun dried tomato pesto on layers of thin slice prosciutto can also work. You can use chestnuts, onions, haggis, olives or sun-dried tomatoes.
You can use chestnuts as a susbtitute. You can use onions instead. Try using haggis or black pudding. Replace with olives, tomato pesto and sliced prosciutto.