Thoroughly wash two 1- cup (250-mL) Mason jars. Fill jars with boiling water. Let stand 10 min. Pour out hot water. Allow to air dry (do not towel dry) .
In large bowl, toss lemon slices with lemon juice, salt and sugar. Cover with plastic wrap. Let stand at room temperature 24 hr. Transfer to jars, seal with lids.
Can be enjoyed immediately or stored refrigerated up to 2 weeks. Decorate with festive ribbons or strings and tags.
Remove lemon slices from brine and finely chop to serve with chicken, fish, lamb, stews and pilafs.