Makes 4 servings
1/2 cup white wine vinegar
1/2 cup distilled white vinegar
1 red onion
6 tablespoons granulated sugar
1 teaspoon kosher salt (or 1/2 teaspoon regular salt)
1/2 cup water
1 long or 2 short cucumbers (seedless if possible)
6 to 8 leafy dill sprigs
Salt and freshly ground black pepper to taste
For the marinade, combine the vinegars, sugar, salt and water in a small saucepan. Bring to a boil, stirring to dissolve the sugar. When it's fully dissolved, simmer for 5 to 10 minutes until the mixture becomes somewhat syrupy. Let cool to room temperature.
While the marinade is cooling, finely slice the cucumbers into rounds about 1/16-inch thick. You can use a mandoline or V-slicer (an angled blade set in a plastic frame; one common one is sold by Benriner), or, if you're patient, you can just slice them with a knife. Pick the leaves from the dill sprigs, discarding the stems, and finely chop.
Place the cucumbers, onion, dill and marinade in a heavy-duty re-sealable plastic bag and refrigerate for at least an hour, preferably 4 or more. With a slotted spoon, lift the cucumbers into a serving bowl and season to taste with salt and freshly ground black pepper.