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Preheat oven to 500 degrees F.
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Grate the zest of one lemon. Cut both lemons into large wedges and set aside.
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Set a small skillet or wide saucepan over medium heat and melt 2 tablespoons butter. Swirl in sea salt and ramps. Turn heat down to medium-low to ensure ramps don't brown at all, and cook until fragrant and very soft, about 4 minutes. Remove from heat and stir in lemon zest.
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Meanwhile, use a fork to whip remaining butter in a small mixing bowl. Fold in ramp and butter mixture and stir well.
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Strain oyster liquor and pour into same pan used for ramps. Cook liquor over medium heat, just until it's reduced by half, 1 - 2 minutes. Stir into ramp butter.
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Fill a rimmed baking sheet just large enough to accommodate all of the oysters with course sea salt or rock salt. Carefully arrange the oysters taking care not to spill liquor. Add a 1/2 teaspoon ramp butter to each, carefully slide into the oven, and cook until oysters are bubbling and fragrant but not at all burned, 8 - 10 minutes.
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Serve oysters with lemon wedges, sea salt, ramp butter, and halved radishes. Leftover ramp butter can be covered and refrigerated for up to 5 days.