Preheat oven to 350 degrees, with racks in upper
and lower thirds. Place dough in the
bowl of an electric mixer fitted with the
paddle attachment. Set a small heatproof
bowl over a pan of simmering water; add
the chocolate, and stir until melted and
smooth. Drizzle chocolate over dough;
mix on low speed until just combined.
Place walnuts in a shallow dish. Form
dough into 1-inch balls; roll balls in nuts,
coating completely. Place balls on parchment-
lined baking sheets. Use your
thumb to make an indentation in center
of each ball. Chill 20 minutes.
Bake cookies in upper and lower thirds
of oven, switching positions of sheets
halfway through, until firm to the touch,
12 to 16 minutes. Remove from oven.
Using the handle of a wooden spoon,
press indentation of each cookie to redefine
shape; fill each with about 1/4 teaspoon
jam. Transfer sheets to wire racks
to cool completely. Store in airtight containers
at room temperature, up to 5 days.
Warming raspberry jam makes it easier to fill thumbprints