Remove the vein from the shrimp, detach the heads, peel the shells, and pat dry with paper towels.

Slice the onion thinly, halve the baby corns lengthwise, and cut the chilies in half, removing the seeds.

Heat olive oil in a pot, add shrimp shells and grated garlic, and sauté over medium heat, crushing the shells as you cook. Add water, chilies, lemongrass, and torn kaffir lime leaves, bring to a boil, cover, and simmer for 15 minutes. Strain the broth.

Return the strained broth to the pot, add chicken stock powder, fish sauce, and lemon juice, and mix. Heat over medium heat, skim off any foam, then add mushrooms, onion, and baby corn. Cover and simmer for 5 minutes.

Add the shrimp to the pot and simmer for 2 minutes.