Misoyaki Steak Frites Skewers (Beef Kushiyaki)

Prep (Up to 24 Hours Before Serving)
1 Make the Misoyaki Glaze: Add sake and mirin to a saucepan and bring to a simmer. Reduce the liquid by one third. Whisk in sugar and miso. Simmer 2 to 3 minutes until thickened. Remove from the heat and cool completely. Transfer the glaze to an airtight container and store it in the refrigerator.
3 Prep the Ribeye: Trim all excess fat from the ribeye. Slice the meat against the grain into very thin strips. Place a piece of parchment paper on top of the strips and pound with the flat side of a meat mallet until the thickness is even.
5 Build the Beef Rectangle: Line a cutting board with plastic wrap and leave several inches of overhang. Vertically place 9 to 10 beef strips, overlapping them slightly to create a rectangle. Layer the next set of strips horizontally on top. Continue alternating vertical and horizontal layers until the rectangle reaches 1.5 inches in height. Fold the plastic wrap tightly over the meat. Place another piece of plastic wrap on top and seal it completely. Press lightly with a rolling pin until even. Freeze for 1.5 hours.
7 Shape and Marinate: Unwrap the semi-frozen meat and trim the edges to create a clean rectangle. Using a sharp knife, cut it into 2 inch rows and then cut those into 2 inch squares. You should end up with about 16. Stack two squares together and skewer them with the cocktail pick to create 8 skewers. Pour half of the misoyaki glaze into a bowl and return the other half to the refrigerator for the pan sauce. Brush a baking sheet and all sides of the skewers with the glaze from the bowl. Cover tightly and marinate in the refrigerator for 12 to 24 hours.
9 Prepare the Shoestring Potatoes: Peel the potatoes. Slice into very thin 1/8 inch planks. Stack the planks and slice them into 1/8 inch matchsticks. Soak the matchsticks in a bowl of ice water in the refrigerator for at least 2 hours or up to 24 hours.
Serving Day
12 Fry the Potato Matchsticks: Fill a small heavy saucepan with 1 to 1.5 inches of oil. Heat the oil to 350°F (175°C). Drain the potatoes and pat them thoroughly dry with paper towels. Carefully add them to the oil and fry until golden and crisp. Using a spider strainer, remove and let cool on paper towels.
14 Sear the Beef: Preheat the broiler. Sear the skewers in a skillet over high heat on all sides until lightly browned. Transfer the skewers to a baking sheet with a wire rack. Brush with more glaze and broil for 3 to 4 minutes until caramelized.
16 Prepare the Pan Sauce: Deglaze the searing skillet with beef broth. Stir in 3 tablespoons of the reserved glaze from the refrigerator and the rice vinegar. Simmer until the liquid is reduced and thickened. Remove from the heat. Whisk in butter and black pepper until melted and smooth.
18 Assemble: Pour the pan sauce onto a serving plate and place the skewers over the sauce. Top with the fried shoestring potatoes and chopped chives.