Heat oven to 350 degrees. In the bowl of an electric mixer fitted with paddle attachment, beat butter and sugar until well combined. Add flour, baking powder, and salt, and beat until just combined. Add eggs one at a time, beating well after each and scraping down the sides of the bowl. Add nuts and craisins, and mix until just combined.
Transfer dough to a baking sheet lined with parchment paper and shape into a 12x3-inch log. Bake 12 minutes; let cool about 10 minutes. Slice diagonally into half-inch pieces.
Place biscotti slices cut side down on parchment-lined sheet and bake an additional 12 to 15 minutes, or until golden and slightly crisp. Cool completely on a wire rack.
In a double boiler, melt chocolate and heavy cream over simmering water. Whisk. Dip end of each biscotti slice in chocolate. Place on a baking sheet lined with parchment paper and chill until chocolate is set.