Peel, wash and cut the potato into 1-inch pieces.
Place in a medium pan and cover with water.
Bring to a boil and cook until tender and soft, about 15 minutes.
Drain the water, and add the vegetable broth or milk.
Use a potato masher to mash the potatoes over low heat.
Remove from heat, add the salt, and pepper, oil and egg yolks. Use an immersion blender to smooth the filling. Set aside to cool for ten minutes.
Preheat the oven to 400F (200C).
Cut one pastry sheet into 3x4 rectangles and gently place them over a baking pan lined with parchment paper.
Use a pastry brush to brush some egg wash over the edges of each rectangle.
Top each rectangle with two tablespoons of the filling.
Cut the second pastry sheet into 3x4 rectangles and use them to top the topped rectangles. Use your fingers to press the top dough gently.
Brush with the egg wash and sprinkle with the sesame seeds.
Bake on the middle oven rack for 22-25 minutes, turning the pan mid-baking.
Remove from the oven and allow them to cook for 5-10 minutes before serving.