1. Slice the cucumbers: Wash the cucumbers and slice them into rounds or spears, depending on your preference. Pack the cucumber pieces into clean mason jars, leaving a little space at the top.

2. Add garlic and spices: Divide the smashed garlic, black peppercorns, mustard seeds, fresh dill, and a pinch of red pepper flakes (if using) between the jars. Nestle them around the cucumbers so the flavors are evenly distributed.

3. Make the brine: In a small pot, combine the water, white vinegar, sugar, and salt. Warm over medium heat, stirring until the sugar and salt are fully dissolved. The mixture should be hot but not boiling.

4. Pour the brine into the jars: Carefully pour the warm brine over the cucumbers in each jar, filling them until the cucumbers are fully submerged. Gently tap the jars to release any air bubbles and add more brine if needed.

5. Seal and cool: Close the jars with their lids and let them sit at room temperature for about 30 minutes to cool slightly. Once cooled, transfer the jars to the refrigerator.

6. Chill and marinate: Allow the pickles to chill in the refrigerator for at least 24 hours before eating. The longer they sit, the more flavorful and tangy they become.

7. Serve and store: Enjoy the refrigerator pickles straight from the jar, or serve them with sandwiches, burgers, salads, or snack boards. Store in the fridge and use within 2 weeks for the best texture and flavor.