Chop the onions and garlic finely.
Chop the plum tomatoes into dices with the seeds.
Slice the heirloom tomatoes into thin slices.
Heat the olive oil in a pot and add the butter.
Add the chopped onions and saute for a minute over a medium heat. Then add the chopped garlic and saute. Just sweat them, do not caramalise.
Add the chopped tomatoes and saute, stirring often, for about 10 mins. We need them to be cooked and thick with not too much moisture left.
Once the tomatoes are ready, season with salt and then add the rose harissa and mix together. Turn off the heat.
Add the cream, grated cheddar and parmesan and mix to combine. Set aside.
Pre heat the oven to 190ºC ( fan assisted )
Remove the tart base from refrigerator.
Spoon the tomato and cheese mix into the tart base and spread.
Decorate the top with the tomato slices.
Bake in the oven for 30 minutes. The crust will be golden once done.
Once ready set aside to cool.
Once it has cooled down a bit, cut and serve.