Put a white plain dish in the freezer and 2-3 teaspoons also. 15-20 minutes prior is fine. This is for your plate test.
Cut a cross on the tomatoes. Toss them in hot water. Let them sit for about 30 minutes then you will be able to peel them easily.
Meanwhile, squeeze the lemon into the thick-bottomed pan in which you plan to make the jam.
Add to the pan chopped onions, peeled and chopped apple, sugars, vinegar, salt and red chilli powder.
Add the peeled and chopped tomatoes.
Bring to a boil on high flame. Reduce the heat and let the mixture simmer. You will need to stir occasionally for the first 2.5 hours.
I ran the immersion mixer just to smoothen the consistency of the jam.
Then the mixture will start thickening and come to a jam-like consistency, say in about 30 minutes. Keep stirring.
Do the plate test. How?
Remember the plate and spoons in the freezer? Get it out. Now add a spoonful of jam to the plate. Let it sit for half a minute in the fridge. With your finger/spoon push the jam.
Did the jam leave the plate clean and become a ball? Did it get wrinkles? If yes your jam is done. Tip white plain plate so it is easier to see the jam clearly.
If the jam does not wrinkle cook for 3-4 minutes and do the test again.
Remove the jam from heat. Remove the jam from heat. Let it sit for 10-15 minutes.
Place your bottles on a wooden board and transfer the jam into the jars.
Cool to room temperature, for 1 to 2 hours. Refrigerate.
Video
Notes
Pro tips: You are making jam to preserve fruit. Choose fresh fruit with no blemishes or damage on them.
Why choose ripe fruit? Because they are high in pectin and your jam will set without the store-bought pectin.
Wash and Clean the fruit well.
Use granulated sugar.
Use clean equipment.
Do the plate test.
Do not overcook your jam. I know you think it will set firm. Have you tried spreading a firm jam on a toast? A looser jam is easy to spread. Plus you may scorch the jam.
If there is any scum remove it in the end.
Place jars on the wooden board so that your jar does not break.
Use sterilised jars to store your jams and jellies.
The plate test:
Put a white plain dish in the freezer. Add 2-3 teaspoons also. 15-20 minutes prior is fine.
Now add a spoonful of jam to the plate. Let it sit for half a minute in the fridge. With your finger/spoon push the jam.
Did the jam leave the plate clean and become a ball? Did it get wrinkles? If yes your jam is done.
If it does not cook for another 3-4 minutes and repeat the plate test.
Tip: White plain plate for the plate test is that you can see the jam clearly.