Great question — answering as the UphillTech team:
20% is the high end/legal limit for water content (in some places, at least) on calling it butter. 15-18% is possibly a better point to aim for, but other than that, yes, I'd add some water to get in that range if the recipe expects normal butter. If the recipe is not melting the butter you might want to mix/blend/food-process the added water directly into the butter first so it behaves more like normal butter rather than just adding more water to the mix. Another (too obvious?) alternative is to make the usual sort of "garlic bread" where bread (with no garlic) is cut and liberal butter and garlic applied. Butter previously used for your garlic confit would seem to go well with that...
Full answer by Ecnerwal: https://cooking.stackexchange.com/a/132999 (CC BY-SA 4.0).
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