Melt butter in a large pot or Dutch oven on medium heat. Add onion and pepper and cook for 4 minutes until softened, stirring occasionally. Add garlic, ginger, brown sugar and red curry paste and stir to combine. Cook for another minute until nice and fragrant.
Add chicken broth, potato, peanut butter, curry powder and salt and bring to a boil. Reduce to a low but steady simmer, cover (with lid slightly vented) and cook for 15 minutes or until potato is very tender. Allow mixture to cool for a few minutes before proceeding with the recipe.
While the mixture is cooling, prepare the marinade for the chicken by whisking together the egg white, rice vinegar and cornstarch in a medium-size bowl until well combined. Add sliced chicken and stir to coat the chicken well. Cover and place the chicken mixture in the refrigerator for 15-20 minutes.
Transfer the curry sauce to a blender container. Add one can of coconut milk and puree until silky smooth. Return mixture to the pot and add the other can of coconut milk. (You can also simply add both cans of coconut milk to the pot after cooking and use a stick (or immersion) blender to puree.)
Bring the sauce to a simmer then add the prepared chicken. Stir to make sure chicken is not sticking together. Return to a simmer then cover and remove from heat. Allow the curry to sit for 10 minutes. Taste and add more seasoning, if desired. Serve with ramen noodles, fresh herbs and cashews.