A sweetly simple little tart featuring rainbow chard and crispy pancetta bits nuzzled in a custard-y filling. Take care to wrap your tart pan with the removable bottom with foil, so you don't accidentally spill your custard base all over the inside of your dear friend aargersi's oven! (I'm pretty sure we cleaned most of it up!) —Ginger's Kitchen
Make the tart dough. Combine the flours, sugar, and salt in a small bowl. Add the cold diced butter and cut in with a pastry knife until the butter is mostly incorporated and only small pebble-sized bits remain. Add 5 tablespoons of ice water to the butter/flour mixture and combine with a rubber spatula. If the dough still seems a bit dry, add an additional tablespoon of water. Use your hands to bring the dough together and shape into a disc. Wrap in plastic wrap and refrigerate for 1 hour.
Preheat the oven to 375 degrees. When the dough has chilled, use a rolling pin to roll it out on a lightly floured surface, until you have a large circle, approximately 1/8 inch thick. Transfer to your tart pan, and cut off the extra bits that extend beyond the rim. Refrigerate for 30 minutes.
Line the chilled tart with foil or parchment, and fill with pie weights. Bake for 20 minutes. Remove the parchment and pie weights and bake ten minutes more, until very lightly golden.
While the tart crust is baking, prepare the filling. Heat a skillet over medium heat. Add the diced pancetta and olive oil, and cook, stirring occasionally, until the pancetta is crispy and has rendered most of its fat. Add in the diced chard, and sprinkle with salt and pepper. Saute for 3-5 more minutes, until the chard has wilted a bit and soaked up the rendered pancetta fat. Set aside.
In a medium bowl, whisk together the two whole eggs plus two egg yolks. Add the milk, cream, salt, and some freshly ground pepper and whisk again to combine.
Transfer the baked crust to a foil-lined baking sheet. Fold the foil around the tart pan to contain any minor(!) filling spills. Arrange the chard and pancetta evenly over the tart crust, and transfer the baking sheet with the tart to an oven rack that has been pulled out. Quickly pour in the egg mixture, slide the oven rack back in, and bake for 45-50 minutes, or until the filling is mostly set and has begun to turn golden brown. Serve warm.