Preheat the oven to 180 degrees C and place the tin(s) on a baking sheet. Roll out the pastry between 2 pieces of cling film, or on a floured surface, and use to line the tin(s), leaving a little excess pastry hanging over the edge. Line with baking parchment and baking beans / uncooked rice or beans / copper coins, and bake for 10 minutes (if making one large tart, it will need 15), then remove the baking parchment and beans (etc.) and return to the oven for a further 5 minutes. Remove from oven and leave to cool. Leave the oven on if you are completing the tarts straight away, or turn off now and preheat again to 180 degrees C later.
Blanch the broad beans - i.e. place in a saucepan of boiling water for 3 minutes, then drain and rinse in cold water to cool down. Remove the pale green cases and discard.
Heat the olive oil in a saucepan and soften the onion for 1 - 2 minutes, then add the courgettes and cook for 2 – 3 minutes. Stir in the broad beans, peas and mint and stir for 2 more minutes. Remove from the heat, transfer to a bowl and leave to cool slightly.
In a jug, beat together the milk, creme fraiche and egg, then add the vegetables and stir. Season. Pour into the pastry case(s), still on the baking sheet to make it easier to transfer to the oven. Fill right up to the edges. Crumble the feta and add, then sprinkle the thyme leaves on top. Bake in preheated oven at 180 degrees C for 30 - 40 minutes (30 for mini tarts, longer for a larger one) until risen and golden. Remove from the oven, leave for 10 minutes, then trim the top(s) with a knife and remove from the tin(s). Serve warm or cold.