Spread one side with 1 tablespoon mustard. Top with 3.5 ounces gruyere cheese, sliced and return for a few minutes to the oven until the cheese begins to melt.
Arrange 5 ounces pastrami slices on top of the other bread slice. Top with the inverted slice with cheese. Serve with potato chips and gherkins, if desired.
For the bread:
Grease one 9x5 inch (23x13cm) loaf pan. Set aside.
In a small bowl mix 1 tablespoon dry yeast and ¼ cup warm water and let foam for a few minutes.
In the bowl of the stand mixer, put 1 cup light rye flour, 1 cup white whole wheat flour, 2 teaspoons salt, ¾ cup buttermilk, 2 tablespoons malt syrup, 1 tablespoon honey, 2 tablespoons sunflower oiland yeast mixture. Mix with a wooden spoon until it integrates.
Attach the dough hook and start mixing on medium-low speed until a shaggy dough is formed.
Add 2 teaspoons caraway seeds, 1 teaspoon fennel seeds and 1 cup bread flour, a few tablespoons at a time.
Beat for 6 to 8 minutes, until the dough is elastic but not too stiff. If it's too sticky add a few more tablespoons of bread flour but don't overdo it. It needs to retain some stickiness.
Transfer dough to an oiled bowl, cover with plastic wrap, and let rise until doubled, about 1 hour. It can take more time depending on the temperature of your kitchen.
On a lightly floured surface, pat the dough down, and then roll it tightly, pinching edges to seal.
Place in the prepared pan, cover with a clean kitchen towel, and let rise again until doubled, about 1 to 1 ½ hours.
About 20 minutes before baking, preheat oven to 375ºF (190ºC).
Bake for 35 to 40 minutes, until golden brown and the bottom sounds hollow when tapped.
Let cool completely on a wire rack before cutting.
Notes
Ratio: The amounts of each ingredient given below are an estimate. Adjust to your personal preference with more of this or less of that.Storing the bread: cover the bread in plastic wrap and store it at room temperature for a few days, in the fridge for a week or frozen for a month (I recommend slicing it first).