Brush the olive oil around the inside of a deep, round 25 cm cake tin.
Season the tomatoes, leave to stand for 10 minutes, then place, cut-side down, in the base of the tin.
Place the flour, baking powder, salt and butter in a food processor and process until the mixture resembles fine breadcrumbs. Add the herbs and milk and process gently to form a soft dough. To mix by hand, rub the butter into the dry ingredients, add the herbs and milk and cut in to form a soft dough.
Turn out on to a lightly floured surface and pat gently to shape into a 25 cm round.
Lay the dough over the tomatoes and bake in a preheated oven at 200 ºC for 35 to 40 minutes until risen and golden.
Leave to stand for 10 minutes before turning out on to a serving plate. Garnish with fresh basil.
Process the basil leaves and garlic in a blender or food processor. Gradually pour the oil into the processor with the blades still running.
To serve, spoon a little dressing over each slice of tart.