Make the custard filling:
- In a medium saucepan, whisk together cornstarch, sugar, and salt.
- Slowly whisk in around 1/3 cup of coconut milk until smooth, then add the remaining coconut milk, almond milk, and vanilla.
- Place the pot over medium-high heat and whisk until the mixture starts bubbling and thickens, about 5 minutes.
- Reduce heat to medium-low and simmer gently, stirring constantly, for 7 to 10 minutes until the custard thickens enough to hold its shape.