Preheat oven to 325°. Butter small tart pans or spray with baking spray.
Combine all shortbread ingredients in food processor and pulse until blended. When you squeeze a bit between your fingertips, it will stay together. Spoon into each tart pan and press along sides and bottom evenly. Bake about 30 minutes - watch carefully during final minutes of baking to avoid burning. Remove to rack and cool.
Meanwhile, prepare filling. Chop chocolate coarsely and place in bowl. Heat cream until small bubbles form around edge of pan. Pour hot cream over chocolate. Stir gently until perfectly smooth. (If it's not, pour through fine strainer). Cover with plastic wrap and refrigerate.
Carefully remove tart shells from pans by inverting onto rack - shells are delicate. Place filling in pastry bag or zip-top plastic bag fitted with star tip and pipe a generous amount of filling in shell. Or use a teaspoon to fill each shell. Refrigerate until serving time.