Don't have lemon, will a little Basil pesto work?

Pesto is never a bad thing.

Pesto is great but then you kinda made pesto pasta. The lemon gives the acidic component to cut through the butter and brighten the dish. If you don't have lemon you could use a splash of balsamic vinegar (white or regular). It's such a simple recipe the butter and broth can be a base for whatever you want. It would be fine without lemon or with lots of Parmesan cheese.

I think that would be a great choice in place of lemon !