Occasional treats & BG

I'm T2, 2 years, on metformin alone, last A1C 6.2. Generally I'm very careful to eat healthy, lower carb meals & to stay away from potatoes, pasta, white flour, etc.
Last week I had a kid-size scoop of butter pecan ice cream (no cone); my BG one hour later: 147. I was surprised, confused & pleased all at once.
I expected ice cream to raise by BG to 200+ and that the experience would serve as a warning not to eat this in the foreseeable future.
Now I'm kind of wondering if I CAN have the weekly ice cream without harming myself. What are your experiences?

I think ice cream is a slippery slope that I prefer to stay away from. Even when I made my own with no sugar I couldn't just eat a single serving. As long as it was in the freezer, it called to me. I might be able to fix that if I made it in some nasty flavor like spinach with blueberries, but it's easier for me to just stay away from it. I don't know what it does to my BS, that might be okay for a single serving once a week, but I can see myself eventually calling a whole quart a "single serving," and trying to convince myself there are only 3 days in a week. Hope it works okay for you, though.

I'll give this additional testing a try.
Re portion control: the kid-size cup at the parlor=enforced portion control.