2) Meanwhile, melt 30g of the butter in a large cast iron frying pan, over a medium-high heat. Stir in the onion, apple, salt and the additional 1/4 teaspoon of pepper, and cook for 7 to 8 minutes, stirring frequently, until light golden brown and tender. Remove from the frying pan and set aside.
3) Divide the pastrami equally between 4 slices of bread; top with the apple and onion mixture and white Cheddar cheese. Top with the remaining bread slices.
4) Melt another 15g of the butter in the frying pan used for the apple/onion mix. Place 2 sandwiches in the pan, place the bottom of a heavy pan on top, and press down to flatten. Cook for 2 minutes, flip, press down with the heavy pan again, and cook an additional 2 minutes, or until the sandwiches are crisp. Repeat with the remaining 15g of butter and 2 sandwiches.
5) Slice the sandwiches in half diagonally. Divide the rosemary-ale jus into 4 small bowls, and serve with the panini for dipping.
A viewer, who may not be a professional cook, provided this recipe. The Food Network Kitchens chefs have not tested this recipe and therefore we cannot make representation as to the results.