Instructions
Step 1
In a food processor, blitz the rolled oats; add in the chopped nuts, a little at a time, continuing to blitz until the mixture is coarse.
Step 2
In a large bowl, use a hand mixer to beat the butter and ½ cup of sugar until the mixture is very fluffy. Beat in the vanilla, cinnamon, and salt. Add in the oat-nut mixture and flour and, using your hands, mix to form a dough. On a clean work surface, shape the dough into a flat disk, then press it into the bottom and sides of a 10½-inch fluted tart pan, forming an approximately ⅛-inch layer all around. Using a knife, trim any dough hanging over the edges and use the extra bits to patch any holes in the dough. Cover the dough in plastic wrap and place it in the refrigerator or freezer for at least 30 minutes to set. (If you must leave it for more than an hour or so, make sure the plastic wrap is tightly sealed to prevent the dough from drying out.) Meanwhile, preheat the oven to 400°F.
Step 3
Bake the tart pan until the crust is lightly golden, 12–15 minutes. Meanwhile, in a large bowl, combine the blueberries, lemon zest, cornstarch, and the remaining sugar. Using a fork, toss the berries vigorously to lightly bruise some of them.
Step 4
When the crust is done baking, remove the pan from the oven and, using a dish towel to protect your knuckles, gently press the crust, which will have risen a bit, back into shape. Pour the berry mixture into the pie crust. If the rim of the crust is already browned, set a protective ring over it (or cover the rim with aluminum foil) to keep it from getting too dark. Transfer the tart pan to the oven and bake until the blueberries are bubbling, about 25 minutes. Remove from the oven and set aside to cool.
Step 5
In a small pot set over medium-low heat, melt the jelly or jam, if using, until the consistency is pourable, 3–5 minutes. When the tart has cooled to room temperature, drizzle the melted jelly or jam over the berries to make a light glaze. Refrigerate the tart for at least 15 minutes. Serve with optional whipped cream or vanilla ice cream.