Step 1Heat the oven to 450 degrees. Melt the butter in a small skillet. In a blender, puree the garlic, 2 chipotles and the adobo until smooth. With the blender running, add the butter. Taste the butter and blend in additional chipotles if desired. Spoon the mixture into a bowl and set aside to cool.
Step 2Spread the rock salt in the bottom of a jellyroll pan. Place the oysters, cup-side down, on the rock salt. Roast until the oysters begin to open, 8 to 10 minutes.
Step 3Remove the oysters from the oven and open them, separating the muscle at the top and the bottom and discarding the flat top shell. Spoon about one-half teaspoon of the chipotle butter mixture onto each oyster and then return them to the oven until the butter melts and the oyster plumps and firms, about 3 minutes. Serve immediately.