Pre-heat oven to 300°F (150°C). Grease a square baking dish (roughly 8 x 6-inch) with butter or ghee.
Bring milk to boil in a stockpot. Lower heat and stir in condensed milk and sugar. Keep stirring on low heat for 15 minutes until the mixture thickens. Remove any milk residue with a slotted spoon. Remove from heat and let it cool for roughly 10 to 15 minutes until it becomes tepid.
In the meantime, in a large bowl whisk the eggs, vanilla extract, nutmeg and ground cardamom till foamy.
Once the milk is lukewarm, slowly stir in the egg mixture. Pour the custard into the baking dish and bake in the oven for roughly 1 hour until the custard is set.
Allow to cool and place in the fridge for at least 2 hours.
Top with nuts and raisins (if using) before serving.