Preheat the oven to 375°F (190°C).
Roll out the vegan pie crust and place it into a tart pan or pie dish.
Lightly prick the bottom of the crust with a fork to prevent bubbling.
Heat olive oil in a skillet over medium heat.
Add sliced leeks and cook for 6–8 minutes until soft and slightly caramelized.
Stir in the minced garlic and cook for 1 minute until fragrant.
In a blender, combine silken tofu, plant milk, nutritional yeast, Dijon mustard, salt, and pepper.
Blend until smooth and creamy to create the custard filling.
Spread the sautéed leeks evenly over the tart crust.
Pour the blended filling over the leeks and spread evenly.
Bake for 30–35 minutes, or until the filling is set and the crust is golden.
Let the tart cool for 10 minutes before slicing.
Garnish with fresh herbs, vegan cheese, or cracked black pepper before serving.