Pre-heat the oven to 200C (180C).
Pour a layer of coarse sea salt into the bottom of a baking tray.
Prick the potatoes with a fork and lay them on the salt.
Cut approximately 1/2cm from the top of the garlic bulb to expose the tops of the cloves.
Place the garlic bulb in the centre of a square of aluminum foil. Drizzle over the olive oil and scrunch the top of the foil over the garlic to form a small parcel. Place the garlic on the same tray as the potatoes.
Bake the garlic and potatoes for approximately 1 hour, or until the potatoes are soft when pierced with a skewer.
Whilst the potatoes are baking, place the butter, chopped herbs, and salt and pepper in a large mixing bowl and stir to combine.
When the potatoes are cooked, remove them from the oven and allow to cool slightly.
Meanwhile squeeze as many garlic cloves as desired into the butter mixture, and stir to combine.
Cut the potatoes in half, and scoop the cooked potato out of the skins and into the mixing bowl containing the butter mixture.
Reserve the empty potato skins.
Mash the potato with the butter mixture, adding as much milk as required to make a smooth mixture.
Fill the reserved shells with the mashed potato. The filled potatoes can be frozen at this point.
Bake the filled shells at 180C for about 20-25 minutes, or until the tops are golden brown and the filling heated through.