Hi.

Usually you get the recipe and end with the cake.

To get something similar as a fluffy/spongy  'angel cake' ;  avoiding eggs... how to come up with a working ingredients list/recipe ?  Baking powder + baking soda + lemon juice (acid) +... ??

Would you do the trial-and-error or there is some guessy science to it ?

 

It depends on context really. If you can identify what an ingredient is doing in a dish, you can probably come up with a reasonable substitute. 

There is such a thing as egg substitute that works reasonably well in baking. Not sure what it’s made of though. 

2 hours ago, Externet said:

Baking powder + baking soda + lemon juice (acid) +

Baking powder and baking soda is (the most of time) the same thing.

https://en.wikipedia.org/wiki/Baking_powder

"Most commercially available baking powders are made up of sodium bicarbonate (also known as baking soda or bicarbonate of soda) and one or more acid salts."

Baking soda + acid + water -> carbon dioxide is released

3 hours ago, Externet said:

Would you do the trial-and-error or there is some guessy science to it ?

Cook's experience plays essential role..A good musician does not have to have staves, to know what tones were played in music.

42 minutes ago, Sensei said:

Baking powder and baking soda is (the most of time) the same thing

No

Baking soda is sodium bicarbonate.

Baking powder is a mixture of baking soda and an acid- traditionally potassium bitartrate.

Saying "Baking powder and baking soda is (the most of time) the same thing" like saying vodka and water are the same thing because vodka has water in it.

3 hours ago, Externet said:

Hi.

Usually you get the recipe and end with the cake.

To get something similar as a fluffy/spongy  'angel cake' ;  avoiding eggs... how to come up with a working ingredients list/recipe ?  Baking powder + baking soda + lemon juice (acid) +... ??

Would you do the trial-and-error or there is some guessy science to it ?

 

Does this help?
https://www.thekitchn.com/the-most-magical-egg-replacement-and-how-to-use-it-234588

 

E x c e l l e n t !  find, John.  It works !  If I did it, anyone can.  Now to add the cake flour, sugar and whatever else hoping to not mess it up.  On my kitchen counter, attached.