Remove the tomatoes from the vine, wash and halve. Preheat an oven to 200°C/gas mark 6. Mix the flour, butter and cheddar in a food processor until the mixture resembles breadcrumbs, then add one lightly beaten egg and mix again until the ingredients form a ball.
Line 4 individual tart cases with the pastry and chill for at least 10 minutes. Line with greaseproof paper, then fill with baking beans and bake for 7-10 minutes until the pastry feels dry. Remove the paper and beans and cook the pastry for a further 2-3 minutes until lightly golden, then remove from the oven.
Make the custard by mixing the remaining eggs with the Dijon mustard, crème fraîche and seasoning. Scatter the halved cherry tomatoes on the base of the tarts and sprinkle over the thyme leaves.
Pour over the custard and bake for 10 minutes. Turn the oven down to 150°C/gas mark 3 and bake for a further 15 minutes until the custard is just set. Cool slightly before serving.