1: Prepare 1 shallot and leave whole. Rinse 750 g tomatoes, dry, then remove the hard stalk end with a small knife.
2: Put the tomatoes and shallot in a centrifuge juicer. This should give you about 500 ml (about 2 cups or just under 1 pint) of juice. Salt and pepper then check the seasoning.
3: Put 4 g gelatin to soften in a bowl of cold water.
4: Pour the tomato coulis into a saucepan and put on medium heat. Bring up to a simmer, whisking gently from time to time.
5: Turn off the heat and add the softened gelatin after draining.
6: Mix well and leave to cool and thicken slightly.
7: Sit a 7-inch (18 cm) tart ring on a sheet of cooking parchment laid on a baking sheet. Note: if your coulis is still runny (if still hot), line the ring with stretch film to prevent it leaking.
8: Pour the coulis into the ring and refrigerate for about 2 hours to set.
9: When set, remove the ring and put the jelly in the the freezer until hard (1 to 2 hours).
11: Put a wire rack on top to stop the pastry swelling too much during cooking.
12: Bake for about 30 minutes until the pastry is a nice golden brown. Leave to cool.
13:
Assembling the tart
Put the pastry base on the serving plate and sit the disc of tomato jelly on top (now you will see why it was a good idea to freeze it beforehand), adjusting until neat. Don't worry about the jelly; it will come back to room temperature in about 10 minutes - the time it will take you to arrange the avocado on the tart.
14: In a bowl, mix 2 tablespoons olive oil, 2 tablespoons lime juice, salt and pepper. This will be the dressing for the avocado slices.
16: Top the tomato jelly with the slices of avocado. Be generous and try to arrange them attractively.
17: Use a brush to coat the avocado slices all over with the lime dressing.
18: Garnish with a few coriander leaves.
Remarks
It is worth taking trouble over your jelly: use really ripe, well-flavoured tomatoes. If necessary, add a little lime (or lemon) juice to the coulis. If you don't have a juicer, you can blend the tomatoes, then pass them through a sieve. If you don't have lime juice, use lemon instead. This tart can be varied by using shortcrust instead of puff pastry.