Wash jars and place them (without lids) in a water-bath canner. Bring to boiling and reduce heat to simmer until ready to use.
Puncture bottom of each tomato with a sharp instrument such as a skewer or fork tine. This helps the pickling liquid flavor the whole tomato more completely. Set aside.
In a non-reactive pot, bring vinegar, tarragon, mustard seeds, lemon or lime juice, sugar, salt and red pepper flakes (if using) to a boil. Remove from heat.
Meanwhile, remove jars to clean cloth or countertop. Place one clove of garlic in each jar and divide dill into each jar. Then pack in tomatoes tightly but being careful not to crush them. Tuck a bay leaf into each jar. Carefully ladle hot pickling liquid into each jar, leaving ½ headspace. Using a bubbler or table knife, loosen air bubbles and re-fill to allowable headspace. Wipe rims, fit lids and bands. Process in water bath for 10 minutes after water returns to boiling. Remove and let cool for 12 hours. Test lids after 1 hour and refrigerate any that have not sealed. Label and date. Store in cool, dark place.
Note: small batches such as this can be refrigerated without water bath processing and will last up several months.
In a 1 quart Mason Jar, puree 1 jar of pickled tomatoes with an immersion blender. Or puree in a blender or food processor. Reduce by 1/3 by heating in saucepan over medium heat. Return liquid to the Mason jar and then blend in olive oil (about 1/2 cup) until emulsified. Add 1 tablespoon capers if desired. Use in salads, over greens and other vegetables.