For a simple assembly just before you plan to serve it, make each component ahead and serve the tart at room temperature.
Sour cream pastry
250g plain flour
A good pinch of salt
200g cold butter, diced
125ml full fat sour cream
Finely grated zest of 1 lemon
A good handful of flat-leaf parsley leaves, finely chopped
Salt and pepper
8 shallots or banana shallots, peeled and sliced in half lengthwise
3 tbsp extra virgin olive oil, plus extra for drizzling
2x 250g punnets mixed colour cherry tomatoes
A few basil leaves, torn if large
Make the pastry, put the flour and salt into a food processor and process for 10 seconds to sift the flour. Add the butter and process until the mixture resembles fine breadcrumbs. Dollop in the sour cream and process until the mixture just comes together. Tip out onto a lightly floured bench and bring together. Cut pastry in half - wrap and put half in the fridge to chill for 20 minutes. Freeze the remaining half for another use.
On a lightly floured bench, roll the pastry into a rectangle, 5mm thick and line a Gobel Oblong Tart Tin. Cover pastry with crumpled baking paper and fill with baking beans. Chill for 30 minutes. Make the filling: preheat the oven to 200°C. Line a large shallow baking tray with baking paper. Combine the ricotta, lemon zest and parsley in a bowl and season with salt and pepper. Cover and chill. Put the shallots in a bowl and drizzle with the olive oil and season with salt and pepper. Tip out into the prepared tray, in a single layer, and put in the oven to roast until completely tender, about 25 minutes. Remove from the oven and transfer to a plate. Tip the cherry tomatoes into the tray and put in the oven to roast until the skins begin to split. Remove from the oven and set aside.
Increase the oven temperature to 220°C. Put the pastry case in the oven and cook for 15 minutes. Remove from the oven and carefully remove the baking beans and paper. Return to the oven for a further 10 minutes to completely cook the pastry. Remove from the oven and set aside to cool a little before removing from the tin. To assemble, evenly spread the ricotta mixture into the pastry case. Top with enough shallots and cherry tomatoes to fit nicely (serve any remainder shallots and tomatoes on the side). Sprinkle with basil leaves and drizzle with olive oil.