Buckwheat shortcrust pastry dough:
Walnut and buckwheat caramel tart:
1Using a wooden spoon, beat together the Earth Balance, confectioners' sugar, and salt until soft and creamy. Mix in the egg yolks until smooth. Add the flour and, using a pastry cutter or a fork, chop up the mixture until it has a sandy texture (if using buckwheat flour, you may need to add more - add this 1 TB at a time). With cold hands, gently shape the dough into a ball, wrap in plastic and refrigerate for at least 1 hour.
2When ready to prepare the tart, preheat the oven to 350F. Grease the tart pan. Roll out the dough between two sheets of parchment paper until ⅛ to ¼ inch thick.
3Line the pan with the pastry and prick with a fork. Cover with another sheet of parchment and pour in pie weights or beans. Bake for 20 mins before removing the parchment and weights. Bake for an additional 10 mins. Remove from the oven and let cool slightly, then remove the pastry shell from the pan (this can be made a day in advance).
4To prepare the caramel, put the sugar and the water in a large saucepan. Heat on high until the sugar melts, without stirring - though you can swirl the pot around if needed. Once the caramel is bubbling and thickens a bit, remove it from the heat and add the cream, molasses, margarine and salt. Be careful: the caramel will steam and bubble. Swirl the pan before returning it to medium heat. Cook for an additional 3 to 4 minutes, or until it reaches 235F.
5Stir in the toasted walnuts and buckwheat and then pour immediately into the tart shell. Spread out the filling and let rest for 10 minutes in room temperature before serving.
6The tart will keep for a week.