To make the filling, combine rhubarb, sugar, and cornstarch.

Let sit for about an hour and stir well from time to time.

To make the crust, mix salt, flour, and sugar in a bowl.

Add coconut oil and orange zest.

Mix with your hands and form into a crumbly dough.

Make sure the fat is incorporated well and there are no lumps of coconut oil remaining.

Grease a springform pan (26-27 cm or 10 inch) with fat.

Preheat oven to 180°C (350°F).

Pour the dough into the pan.

Press into the bottom and the sides of the pan. (Only line about 2.5 cm or 1 inch of the sides with dough. You just want a small border, so the filling doesn't leak.)Set aside.

For the custard, combine soy milk, cornstarch, and sugar in a small saucepan.

Whisk until the starch is dissolved and bring to a boil.

Cook for 1-2 minutes, or until thickened.

Pour over the crust.

Sprinkle rhubarb on top.

Bake for 40 minutes.

While the tart is baking, prepare the marshmallow fluff.

Transfer to a piping bag with a star tip right before the cake is done.

Pipe dollops on top of the tart, increase the temperature to 200°C (400°F) and bake for another 10 minutes, until the meringue is browned.

Let cool completely and remove from pan.