I baked something from the 2014 Canadian Milk Calendar's April page, cheddar onion tea buscuits, but I didn't have cream of tartar nor baking powder, and in a rush I substituted far too much baking powder (double what the recipe called for.) They turned out fine rising-wise, and taste great, until the weird stinging aftertaste (more of an during-feel, I guess) hits you. What could I top these with or dip them in that would counteract that so that I don't have to throw the rest of them out?
They are probably unsalvageable, sorry.
There are two possibilities for the bad taste. If you didn't have much fat in the dough, then what you are getting is probably an alkali taste. It is bland and subtly bitter. Alkali (basic) stuff can be neutralized with acid. But for the neutralization you need to mix your alkalic stuff with acid in a liquid environment. So, you could soak the bisquits in something acidic. But it is almost certain that the cure will be worse than the disease. There is a small possibility that you can get it to work right, if you use a sugar syrup with enough acid. You will get something dripping, revane-like.
In my experience, this kind of dessert is an acquired taste, and you may not like it at all, even if you manage to execute it, and if it works reasonably well (and these are two big ifs).
The second possibility is that you had sufficient fat in the dough to saponify it with the soda. Then you practically got soap in your dough. There is no way to reverse it at all.
Any tries to add something to the bisquits will fail. Humans are very good at detecting bad tastes, even when diluted. You can only try to "remove" the taste, and as described above, your chances for success are minimal.