I think he just discards the potato
NOW you tell me!

I went ahead and made the sauce before you both answered, and I removed the potato, all right. Then I thought I'd taste one of the pieces. Well, it was delicious, so I thought I'd try a second piece. Before you know it, no more potato!
The final sauce was quite brown and quite flavorful. Very unlike KD's. Similar to Pete's 600 ml oil base sauce from the old in2curry days. I worry that all dishes made with this will taste similar, but I assume that's not the case, is it, Stew?
One thing I noticed, and this sounds odd, but it tasted better before I put it in the blender. I should have followed your advice, because the texture was good enough, and it looked better before blending, too. Live and learn!
Anyhow, since the potato (above) tasted so good, I cut up a few potatoes and cooked them in some of the sauce, along with fried garlic and ginger and some peas, and it was very tasty as a side-dish with Indian leftovers from the freezer.