Add the sugar to a pan with 3 tablespoons of water. Let it cook until it boils, then squeeze in the lemon slice. When the sugar turns a caramel color, remove from heat.

Pour the caramel into the mold and let it cool.

Mix the whole milk, sweetened condensed milk, powdered milk (if using), and 2 tablespoons of water. Stir well, then heat over low heat until the milk is steaming. Stir occasionally, then remove from heat.

Beat the eggs until smooth, then gently mix them into the milk mixture in one direction. Strain the mixture through a fine mesh sieve 3-4 times to remove any solids. Pour into the mold and cover with plastic wrap. Place a towel in the steamer basket, bring water to a boil, and put the flan mold in. If your rice cooker is small, you may only be able to cook one at a time. Steam for 5 minutes, then switch the rice cooker to 'warm' for 5 minutes, then back to 'cook' for 2-3 minutes. Remove and let cool.

The flan may look a bit pale in photos, but it's very soft and delicious.