Plums contain enough pectin to turn into jam with only sugar and maybe some lemon juice (for acidity) added, though if you’re doing this the first time you probably want to add extra pectin. Over here that’s generally done by buying sugar that’s laden with pectin, in other places you buy the stuff without included sugar, I recommend to search for recipes on your local internet. If you have a plum tree in front of your window someone in your country will know how to turn supermarket ingredients into jam.
Gelatine in jam is, IMNSHO, a travesty. You’re not making jello.
For 1kg of plums:
Base shortcrust:
(Egg is debatable it’s shortcrust, after all)
For the crumb shortcrust:
Buy good butter with some actual taste from cows eating actual grass, not hyperindustrial stuff fed on nothing but soy it’s worth it.
Mix both doughs individually, wrap them in cling film and chill for at least 30 minutes. A kitchen machine definitely helps with that one note there’s no water (but in the butter), if you use a machine make sure to not overwork the dough. If in doubt, read up on shortcrust.
Halve and seed the plums, then roll out the base dough, laying the plums on top, cut side up. Quartering also makes sense if you prefer but don’t puree them. Crumble the crumb dough over everything, bake at 180C for ~60m.