Peel and slice the pumpkin into medium sized pieces.
Peel and thinly slice the onion.
Slice the garlic.
In a large wok, heat the olive oil. Before oil gets hot, add the sliced garlic and onions. Saute on medium heat for 2-3 minutes. Add the lemongrass leaves and ginger. Stir for a few seconds.
Add the sliced pumpkin. Braise on high heat, shaking the wok every now and then until the slices get a golden brown coating.
At this stage sprinkle sea salt and let this cook uncovered for 5 minutes on low heat.
Add 1/2 cup water, cover and cook the pumpkin now, until it is fully done and falls apart when touched with a ladle.
Remove to a dish and cool. Remove the lemon grass leaves from the cooked veggies and discard.
Once cooled, remove this to a blender and blend to a smooth puree with milk.
Get this back into a saucepan and check for seasoning. The soup will be reasonably thick and very creamy at this stage. Adjust consistency of soup using some water if required, if you prefer a thinner soup.