Cut the porcini in half and, with a sharp paring knife, trim off the inedible parts on the underside of each one.
Slice the caps into 1/4-inch-thick pieces.
In a bowl, whisk together the sundried tomatoes, olive oil, lemon juice, rosemary and anchovy paste. Add the sliced porcini and toss to coat thoroughly.
Let stand for 15 minutes, tossing occasionally.
Transfer everything to a food processor.
With a slotted spoon, transfer the marinated porcini and tomatoes to the processor; puree to a coarse paste, add beef stock to moisten.
Add a little more liquid if the mixture is too thick. Season lightly with salt.
Transfer the pâté to a crock and serve with toasted baguette rounds.