Line a 7½ x 3½ x 2¼ loaf pan with plastic wrap, smoothing it out as much as possible.
Bring cream and butter to a simmer in a heavy bottomed saucepan over medium heat. Reduce to low and add the chocolate. Stir until smooth and shiny. Remove from heat and stir in the ground toasted hazelnuts and the extract.
Pour into the prepared pan. Chill, covered, overnight.
Remove from the refrigerator immediately before slicing thinly, using a hot, wet, knife. Plate immediately before the pâté has a chance to soften.
Can be served alone or with a Raspberry Sauce or Crème Anglaise.