Preheat oven to 375F (190C). Place the pecans on a baking sheet and bake until they smell nutty and are golden, 3 to 5 minutes. Increase the oven to 400F (205C). In a saucepan over medium-high heat, mix the cream, sugar and walnut oil. Bring to a boil, reduce the heat to medium and boil slowly until it thickens slightly, 3 minutes. Remove from the heat, add the pecans and Prunes and stir together. Let stand 15 minutes. Pour the filling into the pre-baked pastry distributing the nuts and prunes evenly.
Bake until the top is a combination of creamy white and russet caramel and looks like rice krispies, 30 to 40 minutes. Cool the tart on a rack for 15 minutes. Loosen the pastry from the sides of the pan with a thin paring knife. Melt the chocolate in the top of a double boiler. With a fork, using a back and forth motion, drizzle threads of chocolate onto the top of the tart, distributing evenly. Cut into squares and serve.