Poach the chicken - season both sides of the chicken breast with salt and pepper, then put it in a small or medium saucepan on a high heat along with the crumbled chicken stock cube or pot, and pour in the cold water. When the water begins to boil, lower the heat to a simmer and cook for 14 minutes (turning once, halfway through cooking). Remove the chicken and set it aside to cool on a plate before shredding. Reserve the stock that the chicken was poached in to add at step 3.
Heat the olive oil in a large frying pan or casserole dish on a medium to low heat. Fry the onion and garlic for 2 minutes, until the onion becomes transparent, stirring occasionally. Pour in the white wine and allow to simmer for 1 minute, or until beginning to reduce down.
Add the diced carrots and cook for a further 3 minutes, while stirring occasionally. Then, add the reserved stock and cream, season with salt and pepper, and bring to a steady simmer. Add the tagliatelle and simmer until the pasta is al dente, stirring frequently to loosen the nests of pasta, about 15 minutes (for dried pasta) and about 10 minutes (for fresh pasta) - you want the sauce to reduce down, but not disappear, so be careful to control the heat.
While the pasta is cooking and the chicken has cooled down, shred it. Add the shredded chicken and defrosted peas to the pasta for the last 5 minutes of cooking. Stir occasionally.
Stir in the parmesan cheese until it melts through the sauce. Remove the pan from the heat and allow it to sit, covered with a lid, for 5 minutes to allow the sauce to thicken.
Serve with extra grated parmesan, freshly ground black pepper and maybe some homemade bread on the side!