Separate 2 yolks from their whites.
Fluff 2 egg yolks till color change, add sugar, beat some more to mix.
Now turn to stir or the slowest mode while adding in 1 1/2 cup of milk.
In another container, stir to fully mix 1/4 cup of milk with 1/2 cup cornstarch, make sure it is free of clumps.
Use a wide sauce pan or wok on medium/low heat, pour the liquid milk/egg into this sauce pan and heat until hot. Do not boil, keep stirring to prevent overflowing.
Add butter to pan then stirring constantly while adding the milk/starch mixture.
Keep stirring (use a balloon whisk might help) to prevent sticking to the pan bottom.
Stirring in circular motion, fold and repeat until it is solidified into custard-like thickness.
Carefully spoon into you mold, use the back of your spatula to spread and even them out.
Let sit to cool off at room temperature, then chill in your fridge for 2-3 hours.