To make the crust, start by preheating the oven to 350°F. Lightly oil a 9 or 10-inch tart pan with a removable bottom and set aside until needed. Place the rolled oats in the bowl of a food processor, and process for at least a minute or two, until the oats have been ground into a flour. Add the pecans, and pulse a few times until the pecans are finely ground and incorporated, but not oily. Add the coconut oil, maple syrup, and salt, and pulse again until the mixture holds together. It will be bit sticky, but will hold together when pressed.
Crumble the pecan-oat mixture into the prepared tart pan, and use your fingers to spread it evenly across the bottom and sides of the pan, pressing firmly. Prick the crust evenly with a fork, then place in the preheated oven and bake for 10 to 15 minutes, until lightly browned. Set aside to cool.
To make the custard, combine the coconut milk, nondairy milk, sugar, vanilla bean seeds or extract, cornstarch, salt, and turmeric in a medium saucepan over medium-low heat, whisking to combine. Use a rubber spatula to stir the mixture slowly and evenly as it cooks, which will help prevent scorching. Allow to cook until the custard is thick and bubbling, which will take approximately 10 to 15 minutes. Pour the custard into a bowl, cover the surface of the custard with plastic wrap to prevent a film from forming, and chill until cold.
To assemble the tart, begin by preparing your chosen fruit. For small berries, simply rinse, pat dry, and use them whole. Strawberries can be used whole if small, or sliced if larger. Nectarines and plums don’t need to be peeled, just pitted and sliced. Because of their fuzzy skins, peaches are best peeled and then pitted and sliced. Regardless of which fruits you’re using, prepare them before assembly and place them nearby your workstation. Spoon the chilled custard into the cooled crust, then spread it evenly with a spatula. Arrange your prepared fruits across the top of the custard in whatever design you like: have fun with it! To give the tart a beautiful glaze, use a pastry brush or crumpled paper towel to dab on the warmed apricot or peach jam, coating each piece of fruit. For best results, serve within a few hours. Leftovers won’t be as beautiful, but they'll still taste scrumptious.
