Preheat oven to 350 °F (180 °F). Grease with butter (or butter-flavor cooking spray) a 12 standard muffin tin or a 6-inch (15 cm) ring mold pan, and sprinkled with sugar (both bottom and sides). Reserve.

Pass the yolks through a sieve to remove their skin. Then, in a large bowl, whisk together the egg yolks, both coconut milk and flakes, sugar, and also the liqueur/extract if desired until mixture is homogeneous. Pour into the prepared pan, about ¾ full.

Bake for 25-30 minutes (muffin tin) or 50-60 minutes (medium ring mold pan for quindão) in a bain-marie, or until top is set and a toothpick inserted into the center comes out clean. For the bain-marie, place the pan in a larger pan with boiling water. Make sure water comes halfway up the side of the quindim pan.

Remove from the oven and let the pan cool down a bit on a rack, about 5 minutes. Place a baking sheet (for quindins) or a platter (for quindão) over the tin or the ring pan and invert the warm custard onto it. It is crucial not to unmold the custard hot, because it will break, or cold, because it will not leave the pan easily. If needed, run a small knife gently around the edges to help unmold the custard. The coconut "crust" will be on the bottom of the dessert once inverted onto a plate.

Let cool down completely and chill in the fridge. Serve chilled by itself or garnished with fresh mint leaves or a dash of grated coconut!