Preheat your oven to 200ºC. Grease two baking trays well.
Place the tomatoes, garlic paste, olive oil and some salt and pepper in a bowl. Toss well to coat the tomatoes in the garlic and oil.
Dust your work surface with a little flour and roll out the puff pastry. Cut out 10cm circles and arrange on a baking tray.
Gather the pastry scraps and roll the pastry out again to make more circles.
Spread half a teaspoonful of basil pesto over each pastry circle leaving a 1cm border around the edge. (Note: you can make the circles bigger or smaller if you wish.)
Divide the tomato mixture between the tarts. Crumble the chevin and dot it over the top of the tomato mix.
Whisk the egg and water together in a small bowl. Brush the egg wash around the edges of the tarts.
Bake the tarts for 25-30 minutes until golden. Drizzle with balsamic reduction if using and serve immediately.