This is the most popular of all Thai soups. This fragrant and flavourful steaming broth is also a favourite here in the US. Sometimes I use shrimp, scallops and calamari rings for a Tom Yum Talay. You can even use firm white fish as a variation, but shrimp or prawn are the most common ingredient.

Ingredients
1/2 lb. medium sized shrimp, shells removed and butterflied
3 stalks fresh lemon grass-bruised and slit and cut in half
3 cups water, shrimp or fish stock
fish sauce (nam plah)
4-6 slices fresh galanga (kah)
4-6 fresh kaffir lime leaves (bai magrood)
1 cube Knorr Tom Yum Soup base
2 tsp jarred Tom Yum Soup Base
1 small red onion cut into 1" pieces
1 cup fresh small white mushrooms, cut in half
1 can whole straw mushrooms, drained
2 small tomatoes, cut in quarters

Finishing Soup
2 green onions, cut in thin slices
cilantro sprigs for garnish
Juice of 1-2 limes, to desired sourness
Fish Sauce for desired saltiness

To make stock:

Add 6 cups of water to a stock pot, add empty shrimp shells, lemongrass, and kaffir lime leaves. To prepare lemongrass-remove outer hard leaves, cut off the top third and the bottom root, small several times with the back of a clever to release the fragrant oils, cut in half then slit each half down lengthwise. Add the sliced galangal and kaffir lime leaves.

Bring to a boil, then reduce heat to low and simmer for 20-25 minutes to make a nice stock. Strain out the shrimp shells and lemon grass.

Add the Knorr cubes and Tom Yum paste, stir until disolved, taste and adjust flavours. Simmer a couple of minutes. Add the onion and mushrooms. Bring to a simmer, add the onions. Simmer for a couple of minutes. Add in the tomato wedges and shrimps. After 30-35 seconds, turn off heat, add lime juice to the desired sourness and fish sauce to attain the proper saltiness.

Do not let the prawns or shrimps overcook.

Serve immediately.

Garnish with green onions and cilantro sprigs. Offer guests fish sauce, chopped chiles and lime wedges to adjust to their taste.