Mix flour, yeast, sugar, and salt in a bowl.
In a mixing bowl, combine warm milk, custard powder, water, and melted butter.
Add milk mixture to the bowl with the flour mixture. Beat with a dough hook on low speed for 1 – 2 minutes until combined; scrape down the sides of the bowl with a rubber spatula. Increase mixer speed to medium, continue kneading until the dough comes together and pulls away from the sides of the bowl and no longer sticky, about 5 – 8 minutes. Note: Make sure to knead the dough long enough, so your bread is light and fluffy and not dense or heavy. Heavy bread can be the result of not kneading the dough long enough. See note for by hand instructions.
Lightly spray a clean bowl with cooking spray and place the dough in the bowl. Cover with plastic wrap or a clean kitchen towel. Let rise in a warm place until puffy and doubled in size, about 1-2 hours.