Cut the cucumbers on a mandoline into ¼-inch slices. In a large bowl, toss the slices with the salt until combined. Cover with just enough ice to completely cover and let sit for 3 hours. The ice will be mostly melted by the end.
Drain the cucumbers and transfer to a nonreactive bowl. Add the onion, garlic and dill and toss to combine.
In a medium pot, combine the vinegar, 1 cup water, sugar, mustard seeds and black pepper and bring to a simmer over medium-high heat. Once the sugar has dissolved, pour the mixture over the cucumbers and let everything cool to room temperature. Divide the pickles and their pickling liquid evenly among 4 clean pint jars. Screw on the lids fingertip-tight, then refrigerate for at least a day.
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