Begin by sterilizing the canning jars to ensure your pickles are safe to store. Place the jars in a pot of boiling water for 10 minutes, then remove and let them air-dry on a clean towel. Simultaneously, heat the snap lids in a separate pot of simmering water (not boiling) to soften their sealing compound. Keep both jars and lids hot until you're ready to use them.
Rinse all of the mixed fresh vegetables thoroughly under cold running water, then drain well. Trim any stems or ends, and cut or slice each vegetable variety into bite-sized pieces to ensure even pickling and easy eating. I like to use a mix of carrots, cauliflower, cucumbers, and bell peppers, but you can use whatever vegetables you love most.
To each hot, sterilized canning jar, add 1 tablespoon of pickling salt, 2 large garlic cloves, 1 head of fresh dill (or 1 teaspoon dill seeds), and ½ teaspoon whole black peppercorns if using. Layer the prepared vegetables into each jar, packing them tightly and gently shaking the jar after each layer to fit as many as possible. Fill each jar to within 1 inch of the rim.
In a medium saucepan, combine the white vinegar and sugar. Heat the mixture over medium-high heat, stirring occasionally, until it comes to a boil. Boil uncovered for 5 minutes to dissolve the sugar completely and form a tangy, sweet brine.
Pour 1 cup of the hot vinegar solution into each jar filled with vegetables. Then, fill each jar with boiling water, leaving about ½ inch of space at the top. This combination ensures the vegetables are fully submerged and evenly pickled. I like to use a ladle and a canning funnel to help reduce spills and burns.
Wipe the rims of each jar with a clean, damp cloth to ensure a good seal. Top each jar with a hot metal lid and screw the ring on until it's just finger-tight. Process the sealed jars by submerging them in a boiling water bath for 15 minutes, or in a preheated 310°F (155°C) oven for 15 minutes, as preferred. Remove jars and let them cool undisturbed on a towel.
Let the processed jars sit at room temperature for at least a week before opening. This resting period allows the flavors to fully penetrate the vegetables for the best-tasting pickles. For extra flavor, I sometimes add an extra sprig of dill right before sealing the jars.