Skin and chop tomatoes and place in pot with the sugar, few cloves (like 3 or 4)and lemon slices, cooking on a medium heat about 20 minutes or so, until thickened. Watch it closely so it doesn't burn, stirring constantly.
Fill small jars that have been sterilized with the hot jelly, wipe off the rims and apply the seals and lids. Place on counter to cool and listen for them to seal.
I added a package of pectin because, if I remember right, it is a very thin consistency, like almost too thin and it needs to be thickened up a bit.