PR#1: dough PR#2: toppings

You first send PR#1, then PR#2 on top of the first one.

The diff for PR#1 will show dough stuff. The diff for PR#2 will show toppings in relation to dough.

People can review them asynchronously. If you merge PR#1, PR#2 will automatically target main (that's where dough went) now.

In this arrangement, I use to cross-mention the PRs by number (a link will exist in both). I also like to keep the second one draft, but that depends on the team practices.

I don't understand why you would close the second PR when the first gets merged. It should lose the dependency automagically, which is exactly what happens if you branch correctly.