To prepare the beef tenderloin pops, preheat the oven to 400°F.  

Heat a large cast-iron fry pan over high heat for 5 minutes. Pat the steaks dry with paper towels and brush all over with the olive oil. Season the steaks all over, including the sides, with the salt and black pepper. Sear the steaks in the hot pan, top bottom and sides evenly, about 2 minutes per side.

Transfer the steaks to a baking sheet; set the fry pan aside to use for the glaze. Roast the steaks in the oven until an instant-read thermometer inserted into the thickest part of the meat registers 125°F for medium-rare, 8 to 10 minutes. 

Remove from the oven, cover the baking sheet tightly with aluminum foil and let rest for 10 minutes. Transfer the steaks to a cutting board and cut into bite-size pieces. Thread the pieces onto skewers.

To prepare the glaze, in a sauté pan over medium heat, melt the butter. Add the mushrooms and cook, stirring occasionally, until starting to soften, 4 to 5 minutes. Add the sherry and cook, stirring occasionally, until the mushrooms are tender, about 10 minutes. Sprinkle with the salt and black pepper. Remove from the heat.

Without wiping out the pan used to sear the steaks, add the olive oil to the pan, set over medium heat and add the shallots. Cook, stirring occasionally, until starting to soften, about 2 minutes. Add the brandy and deglaze the pan, stirring to scrape up the browned bits, until the brandy has evaporated and the shallots are tender, about 2 minutes. Stir in the mushrooms and cream and simmer until thickened, 4 to 5 minutes. Stir in the mustard and adjust the seasoning with salt and black pepper.

Coat the skewered beef with the glaze and sprinkle with the parsley.

To prepare the macaroni and cheese, preheat the oven to 375°F.  

In a fry pan over medium heat, melt 2 tablespoons of the butter. Add the onion, season with salt and cook, stirring frequently, until softened, 4 to 5 minutes. Remove from the heat.

In a food processor, combine the bread and the 3 tablespoons chilled butter and pulse until coarse crumbs form, about 10 pulses. Set aside.

In a large pot over high heat, bring 4 quarts water to a boil. Add 1 tablespoon salt and the macaroni and cook according to the package instructions. Drain well.

In the same pot used for the macaroni, melt the remaining 6 tablespoons butter over medium-high heat. Add the flour, dry mustard, 1 tablespoon salt and the cayenne and cook, whisking constantly, until the mixture is fragrant and deepens in color, about 1 minute. Gradually whisk in the milk and bring to a boil, whisking constantly. Reduce the heat to medium and simmer, whisking occasionally, until thickened, about 5 minutes.

Remove the pot from the heat and slowly whisk in the Monterey jack, Gouda and Gruyère until completely melted. Add the onion and stir to combine. Add the macaroni to the sauce, return the pot to medium-low heat and cook, stirring constantly, until the mixture is heated through, about 6 minutes.

Transfer the macaroni mixture to a 9-by-13-inch baking dish and sprinkle with the bread crumb mixture. Bake in the oven  until the crumb topping is golden, about 15 minutes, checking often.

Serve the macaroni with the beef tenderloin pops.