Saute the frozen fries for 12 to 15 minutes in a large skillet with duck fat over medium heat until crispy. Season to taste with salt, pepper and caraway seeds. Set aside.
Bring water to a light boil in a medium saucepan. When the water is boiling, immerse the bags of smoked duck meat in it (without opening them) and turn off the heat. Let stand 4 minutes.
Meanwhile, brush 4 slices of rye bread with old-fashioned mustard and place one per plate. You can lightly toast the slices of bread beforehand.
Remove the bags of smoked meat from the pan and open them. Transfer the duck meat to a bowl and divide it evenly over the 4 slices of bread.
Cover each sandwich with a slice of bread brushed with a little old-fashioned mustard.
Serve immediately with duck fat fries, coleslaw and quartered pickles.
