Halve the leek lengthwise and thinly slice pale stem, discarding any dark green stem (see cooking tip). Peel the carrot, then cut into 1cm chunks. Thinly slice the garlic. Discard the husk and silks from the corn, then break or cut the cob in half. Crumble the stock cubes into a large heatproof jug, add 1.5L (6 cups) boiling water and stir to dissolve.
Step 2 — Cook vegetables
Heat 1 tbs oil in a large saucepan over medium-high heat. Cook the leek, carrot and garlic, stirring regularly, for 4-5 mins until softened. Season with pepper.
Step 3 — Simmer soup
Add the corn cobs, chicken and stock to the vegetables and bring to the boil. Reduce the heat to low and simmer for 45 mins or until the chicken is tender and cooked through.
Step 4 — Prep tarragon
Meanwhile, pick the tarragon leaves, discarding the stems, then coarsely chop.
Step 5 — Cook noodles
Using tongs, remove the corn cobs and chicken from the soup. Increase the heat to high and bring the soup to a simmer. Add the noodles and cook for 2 mins or until tender. Taste, then season with salt and pepper.
Step 6 — Get ready to serve
While the noodles are cooking, slice the kernels from the corn cobs. Shred the chicken using two forks. Divide the corn and chicken among bowls and ladle over the noodle soup. Scatter over the tarragon to serve.