Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish.
Mix the batter: In a large bowl, combine grated cassava, coconut milk, condensed milk, evaporated milk, eggs, sugar, melted butter, and vanilla. Stir well until smooth.
Bake the cake base: Pour mixture into the prepared dish and bake for 45–50 minutes, or until the cake is firm and slightly golden at the edges.
Cook the custard topping: In a saucepan, whisk condensed milk, evaporated milk, egg yolks, and flour. Cook on low heat, stirring constantly, until thickened (about 8–10 minutes).
Add the topping: Spread custard evenly over the baked cassava base.
Bake again: Return to oven for 15–20 minutes, until the top is golden brown.
Cool and serve: Let the cake cool before slicing. Serve warm for gooey texture, or chilled for a firmer bite.