To make dulce de leche, put all the ingredients (milk, cream, sugar, salt, baking soda, and vanilla) in a medium saucepan or pot. Bring it to a boil, and let it simmer for 60-90 minutes, until it caramelises and thickens into a thick peanut-butter-like paste.
Pour the dulce de leche onto a lined baking tray, or a silicon mat, and tilt the tray around so that it forms a circle (roughly 6 inches in diameter). Then put this in the refrigerator or freezer for 30 minutes to an hour to harden up.
Now onto the tapioca cake. First, peel and grate the tapioca, and squeeze out the excess liquid from the grated tapioca. Add the egg yolks, caster sugar, brown sugar, salt, coconut milk and pandan leaves to the tapioca. Then mix it well using your hands, making sure to squeeze and twist the pandan leaves to release its aroma, then remove the pandan leaves.
Ready a well-oiled medium frying pan. Cut a piece of banana leaf into a circle the size of the bottom of the pan, and place it in the pan. Oil the top of the banana leaf, and pour half of the tapioca cake mix into the pan. Place the disc of hardened dulce de leche on top of the first layer of tapioca, and then top it off with the rest of the tapioca cake mix.
Bake this in an oven preheated to 170°C for 60 minutes. Then, flip it out onto a lined baking tray and bake for a further 30 minutes, until the top turns nice and golden. If it doesn’t release from the pan easily, run a spatula or a small knife along the sides of the pan to help the cake release.
When it’s done baking, let it cool for at least 30 minutes, letting the dulce de leche filling set a little. Then, using a serrated knife, slice it up into pieces and serve!