Preheat oven to 375 degrees. In medium bowl, combine whole wheat and all-purpose flours. Stir in olive oil and cold water, just until the dough forms a soft ball. Gently press dough into the bottom and sides of small oven-safe baking dish and poke a few holes into the dough using a fork. Bake 13 to 15 minutes, or until lightly browned. Remove from oven and set aside, then increase the oven temperature to 425°F.

While the crust is baking, heat 2 teaspoons of olive oil in a large pan on medium until hot. Add the garlic, white parts of the spring onion and asparagus. Season with salt and pepper and cook, stirring occasionally, 3 to 4 minutes, or until the asparagus is tender and the onion is slightly softened. Let cool.

In a medium bowl, whisk together the eggs, lemon zest, whole grain Dijon mustard, milk and all but a pinch of the cheese. Season with salt and pepper. Add cooled vegetables to the filling and pour mixture into the pre-baked crust. Sprinkle remaining cheese on top of tart and bake 20 to 22 minutes, or until the filling is completely set and the top is browned. (Cooking times may vary depending on the size and depth of your baking dish. The shallower your dish, the faster the baking time will be.) Remove from the oven and let stand for at least 5 minutes before serving. Garnish with parsley leaves.