Preheat your oven to 325°F (163°C). Get out a large saucepan and pour your milk into it.
Heat the milk over your stove on medium-low heat until it simmers and bubbles start to form around the edges.
Get out a medium bowl and whisk together the eggs, yolks, sugar, salt, and vanilla until evenly combined. Pour the heated milk in after and whisk again.
Pour the mixture in your casserole dish/oven-resistant small cups, making sure it gets strained with a strainer while pouring. Add in ground nutmeg/cinnamon.
Fill the mixture with hot water until the casserole dish reaches 1 inch from the top. If you are using small cups, fill the cups with hot water until they reach about halfway from the top.
Place the egg custard in your preheated oven and bake until the custard sets, which should take around 40-45 minutes. Do not bake longer than 45 minutes.
Take out the custard when it becomes soft and firm. Let it cool for 5-10 minutes before serving.