How frequently can I expect to cook "special" meals?

Rupees are kinda hard to come by in this game surprisingly, but apples aren't. So I've been taking up all my excess apples and cooking them together to sell back (from 3RPA to 10RPA cooked). There was one time while cooking Simmered Fruit (5 apples), the music played back was slightly different and I managed to cook a "special" Simmered Fruit.

It's "special" in that it looks exactly the same as the regular Simmered Fruit dish and has no distinctive look or description (and costs the same) but it heals 8 hearts rather than the usual 5.

How often can I expect this to happen?

It seems to be pretty random, from what I've been able to find. From this page:

Recipes may acquire random bonuses, such as being boosted from low to mid or have extra hearts. The jingle heard is altered when the results are randomly improved.

This site also says that it is random and that it will apply one of a few different effects to your dish.

On top of these buffs, when cooking you may also hear a special sound. When this happens you will receive an extra bonus at random. These are:

• Extra yellow heart
• Three extra hearts
• Buff increase by a further 5 minutes
• Buff increased by +1
• Stamina increases

However, this article also says that there is a way to guarantee this boost.

You can actually guarantee these bonuses by using particular items or cooking during a certain time.

Cooking during a Blood Moon, when the moon is red and enemies respawn, will give you a random bonus. As will using a star fragment or dragon body part in your recipe.

Thus, it's not yet known the exact chance to have this bonus happen to you, but you're able to force it to happen by cooking under certain conditions or using certain ingredients.