This is the very first thing I recall learning to cook at 6 years old in Panama City, Florida. We had two cooking-pear trees that were constantly being raided by squirrels and tiny fruit-bats. So the idea was to get the pears first before the critters did.
This can be a sandwich-jam or (as was done at my home) it can be chilled and then served in a bowl at family gatherings as a kind of side dish. It's VERY sweet and delicious.
NOTE: This is canning. Hot, sterile jars will be needed, but if you intend to make no more than the amount given then it'll probably get eaten pretty quickly.
Peel and core pears; cut the pieces into bite-sized chunks or half that size if you plan on using this more for sandwiches. Discard peel and cores.
Place sugar, lemon juice and water in a heavy-bottomed pot at least four times as deep as what fills it; stir well until all sugar has dissolved (important!)
Add pears and bring mixture slowly to the very beginnings of a slow, gentle boil, stirring occasionally as it heats. When it begins to boil, drop the heat down to a low simmer and lid the pot.
Stir OFTEN, making sure that the preserves do not burn (and they will, given a chance! But don't stir too enthusiastically unless you're wanting this to be more for sandwiches.) Sometimes more water is needed depending on the dryness of the pears; if they seem to be getting too thick and sticky, add a little. It will all cook down.
NOTE: Cooking-time given is variable! What you're waiting for is for the pears to turn translucent; they should deepen in color somewhat also, depending on the type of pear used (some become a golden brown, some remain pale.) When they've become translucent and the liquid with them has thickened to the consistency of thin syrup, remove from heat.
Pour the mixture evenly into heated, sterile canning jars; as this is NOT a lesson in canning, I won't go into all the specifics of canning the preserves (please look up elsewhere!) Make sure that some room is left in each jar, as preserves will expand.
If serving in proper NW Florida style, keep a jar in the fridge at all times and occasionally serve along with baked chicken, turkey, ham or any other meal with a lot of meat; the cold sweetness is welcome.