Preheat oven to 450 degrees.
First, make the mashed potatoes. Add potatoes, broth, and a teaspoon of salt in a pot. Turn heat to high and as soon as the broth starts to boil time 10 minutes and then drain and put potatoes back in the pot.
Next, add butter and a 1 teaspoon salt/pepper to the potatoes and mash. When mashed add sour cream and chives and mix. Set aside to let potatoes cool.
Now, place sausage on a sheet tray and drizzle with oilve oil so the sausge crisp up in the oven. Place in the oven for 20 minutes. Then set aside to cool.
Next, roll out both sheets puff pastry 1 inch more then it is and divide each sheet of puff pastry into 4 strips (8 strips of puff pastry). Brush mustard on one side.
Next, add mashed potato to four strip of puff pastry, then add a sausage link on top of the mashed potato, and then add mashed potato around the top of the sausage. Now, place another strip of puff pastry (Dijon side down) ontop and seal all the edges.
Repeat this to make 4 Wellingtons (you can make double and freeze half at this point for a future dinner by doubling the recipe).
Now, add all the Wellingtons to a sheet pan and brush with egg and sprinkle sesame seeds ontop.
Finally, place on middle rack for 20 minutes and enjoy!