Wash two 1-quart jars and lids with hot soapy water and rinse well. Trim 1/8 inch from the blossom end of the cucumbers, then cut into spears or 0.5-inch rounds.
Divide the fresh dill, garlic, black peppercorns, mustard seeds, coriander seeds, red pepper flakes, and bay leaves between the jars, then pack the cut pieces in tightly, leaving about 0.5 inch of headspace.
Combine the water, distilled white vinegar, kosher salt, and granulated sugar in a small saucepan; bring to a boil over high heat, stirring to dissolve, 2–3 minutes. Remove from the heat.
Carefully pour the hot brine into the jars to cover, maintaining 0.5 inch of headspace. Tap the jars gently and use a clean utensil to release air bubbles; top up as needed.
Let cool uncovered at room temperature until just warm, about 1 hour, then seal the jars and refrigerate.
Refrigerate until the flavors have penetrated, 24–48 hours. They are ready when the color turns from bright to olive-green and the flavor tastes balanced with a crisp snap; keep refrigerated and use within 1 month.