Preheat the oven to 400 F.
Cut the mushrooms into bite-sized pieces, toss with the oil and salt and lay out on a baking sheet or large (12 inch) cast iron skillet.
Roast the mushrooms for 25 minutes, then push the mushrooms to the side of the pan to reveal a cooking surface, add the garlic, and bake for 2 minutes more.
Remove the pan to cool completely.
Transfer the cooled mushrooms to a food processor and blend to a coarse, spreadable paste, pulsing and drizzling in about 2 tablespoons of the oil.
Transfer the mushroom spread to a bowl, add the rest of the oil and the chopped truffle and season to taste with salt (I usually add an extra ¼ teaspoon). It should be well-seasoned with salt.
Pack the tartufata into 1 pint jar or two half pint jars, pressing the mushrooms down to remove air pockets.
Top the jars off with ¼ inch of additional oil to completely cover the mushrooms. Screw on a lid and refrigerate for up to 2 weeks. The mixture can also be frozen.
