The best shapes for porcini mushroom
Porcini sliced and cooked in fat, sometimes finished with cream. The slices stay wide and flat and keep their texture, so the dish is really a sauce built around one large solid element rather than many small ones.
Porcini cooked down in fat, with or without cream. The slices need width to rest on, egg ribbons are the habitat.
Canonical: pappardelle, fettuccine, tagliatelle.

Butter and cheese emulsions need surface, not pockets.

Width is the whole argument.

The fluted, crimped border and broad flat face give a meaty or creamy sauce many edges to cling to.

A long strand with a squarish, slightly rough section holds a clinging sauce along its length.

A thick rough square strand carries weight and clings to dense sauces, so the traditional dressings are hearty.
What we would not put it on
Small tubes. A mushroom slice is wider than the shape itself, so the two never combine on the fork and are eaten in turn.
Want it the other way around? Start from a shape in the Pairing Finder.
Stay in the loop
From the Almanac
Updates from Pasta Almanac, when there is something worth sharing.