Answer:
Hopefully you have the exploded parts diagram - it was on the back cover of the manual/paperwork that came with the faucet. If not, the company has a decent set of manuals & parts diagrams on their site. I have a Bernini model, and I also saw an Ashfield that had the same setup.
On your parts diagram, you'll see part #975-012 - that's the restrictor. You can do all of this from above the counter. Really you just have to dig your way down to it. Don't forget to turn off the water supply!!!
1. Remove the handle. The set screw on mine used a 3/32 Allen key, and it's way in there, so this part is a little slow and frustrating since you blindly have to find the keyhole. I used a tiny mirror & flashlight to see where I was going - at least to get started.
2. Now unscrew the top trim ring by hand. There's no real way to use a tool for this without damaging a thread or the finish.
3. Next is the brass piece (collar?). You need a large wrench or adjustable wrench, and it's on there pretty snug. Might be a good idea to mark the position of it before you take it off - use a wee bit of masking tape. It is a normal thread, not backwards.
4. You should now be able to pull out the cartridge. Below you'll see the little grey culprit. Before you go after that, check and see if the gasket/O-ring is still below or it it came up with the cartridge. If it's below, remove it carefully with some tweezers and set it into the grooves of the cartridge. Don't damage this part - if so you need a new one.
5. The restrictor is in there pretty good - you need some fine needlenose type pliers to get a grip on it, and not damage the metalwork, but ultimately just yank it out.
6. Reassemble and enjoy!