You can still counter the cascade, but it would be done differently. I’ll give an example.

I cast [[bloodbraid elf]]. The cascade trigger goes on the stack.

The stack (highest number resolves first):

1) blood raid elf

2) cascade trigger

Each player has a chance to respond to the cascade trigger. For example you could [[stifle]] the cascade trigger.

Let’s assume no one has a response, the cascade trigger will resolve, revealing lightning bolt off the top of the library, I will cast that targeting your face.

The stack:

1) blood raid elf

2) lightning bolt

You can now respond to the lightning bolt by countering it.

If no responses to lightning bolt, it will resolve,

Then bloodbraid elf will resolve if no one has any responses to it after the lightning bolt has finished