For pressure cooker: Add potatoes and 6 cups of water to Instant Pot. Close lid and set manual time for 4 minutes. Once cook time complete, quick-release pressure. Pour potatoes into a colander, then transfer to a sheet pan to cool.
For stovetop: Add potatoes to a large pot and cover with water. Bring to a boil, then reduce heat to medium-low and simmer for about 10 unites - until barely tender. Transfer to a sheet pan to cool.
In a large mixing bowl - add mayo, Dijon, lemon juice, dill, salt, and pepper and whisk to combine well.
Then add potatoes to bowl and gently mix until fully combined.
Refrigerate for a few hours before serving.