Open the scallops with a knife by running it flat against the shell and then remove the scallop meat, trim off any sinew to leave just the white meat and the brightly coloured orange roe. Rinse the scallops and roe under cold water, drain and set on kitchen paper. Place them in the fridge, and wash both shells out thoroughly.
To make the ratatouille,
Chop the courgettes and aubergine into even-sized 2cm pieces, put in a bowl and sprinkle with salt, leave for 10 minutes to remove excess water. Then rinse and dry on kitchen paper. Peel the peppers and remove the seeds, chop into even-sized pieces, as the courgettes, but keep separate.
Heat a large saucepan, peel and chop the onion and add to the pan with a little olive oil and the crushed garlic.
Take the bottom scallop shell and put a spoonful of the ratatouille into the shell, place a scallop and the roe on top, season with salt and pepper and a little olive oil, and cover with the top shell.
Roll out the puff pastry and cut into four strips long enough to go around the scallop shell. Run the pastry around the shell to seal it fully, then brush with the egg yolk.