Kosher salt and fresh ground black pepper to taste
Mild cooking oillike grapeseed or canola
Using a paring knife, clean out the cavity of the lobster mushrooms, taking off a little extra trim than usual to fit more stuffing.
In a saute pan, melt the butter, add the diced lobster mushrooms and cook until lightly browned, seasoning them lightly with salt and pepper. Add the shallot and garlic and cook until translucent, about 3-4 minutes. Add the panko and herbs, stir to incorporate, then allow the stuffing to cool. After the stuffing has cooled, stir in the chopped whelks or whatever you're using, and the egg and yolk. Double check the seasoning for salt and pepper (cook a tbsp or so if you're scared of raw egg) and reserve.
Next, heat a saute pan with some oil until lightly smoking. Brown the lobster mushrooms lightly on each side to deepen their flavor, then allow them to cool until they can be handled, you do not need to cook them through since they will bake in the oven.
To fill the mushrooms and roast, season the lobster mushrooms inside and out lightly with salt and pepper, then pack them full of stuffing, top with breadcrumbs, then with lobster mushroom butter and herbs and roast at 375 for 25- 30 minutes, or until completely cooked through.
A quick note on equipment: I used an ebilskiver pan in the pictures to steady the mushrooms in the oven so they don't tip. Some pie weights, crumpled aluminum foil, or something similar would work too.