Start by making the crust. Add oats, almond meal, cornstarch and sea salt to a medium bowl, whisking to combine. Add coconut oil, honey and vanilla to the bowl, then mix together using a fork. Transfer the dough (it will be crumbly) to an 11-inch tart pan with removable bottom. Press the dough evenly across the bottom and up the sides of the tart pan. If the dough gets sticky, you can use the bottom of a measuring cup to press and flatten. Cover with plastic wrap and chill in the fridge for 30 minutes.

While the dough is chilling, prepare the almond custard. Add sugar, sea salt, cornstarch and egg yolks to a medium bowl, whisking until well-combined. Warm almondmilk in a medium saucepan over medium heat, stirring occasionally, until steam starts rising off the surface and small bubbles form around the edge. Don’t let this come to a boil.

Take the almondmilk off the heat, and slowly pour half of it into the egg mixture, whisking the eggs as you pour. This is called tempering. Pour the tempered egg mixture into the saucepan with the remaining almondmilk, and return heat to medium. Let cook, whisking constantly, until thickened (about 2 minutes). Take the saucepan off the heat and whisk in coconut oil and vanilla extract. Pour thickened custard into a bowl, and immediately cover the surface with plastic wrap, making sure the plastic is in direct contact with the custard. Let cool to room temperature, then chill in the fridge for at least 2 hours.

While the custard is chilling, finish the crust. Preheat an oven to 350°F and set an oven rack to the middle position. Using a fork, poke holes all over the bottom of the chilled crust. Place the crust on a rimmed baking sheet, and bake until golden and fragrant (20 - 25 minutes). Transfer the crust to a cooling rack, and cool completely before filling.

Spoon the chilled almond custard into the cooled crust, and using an offset spatula, smooth the top. Scatter berries all over the top of the tart, piling higher in the middle and leaving some custard showing around the outer edge. Finish with a sprinkling of small, picked mint leaves.