• Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce. • Cut potatoes into 1⁄2-inch-thick wedges. Trim and thinly slice mushrooms (skip if your mushrooms are pre-sliced!). Halve, peel, and thinly slice onion. • In a small bowl, combine mayonnaise with horseradish sauce; season with salt and pepper.

• Toss potatoes on a baking sheet with 3⁄4 tsp garlic powder (1 1⁄2 tsp for 4 servings), a drizzle of oil, salt, and pepper (reserve remaining garlic powder for another use). • Roast on top rack until browned and tender, 20-25 minutes.

• Meanwhile, heat a large drizzle of oil in a large pan over medium-high heat. Add mushrooms and season with salt and pepper. Cook, stirring, until lightly browned, 4-5 minutes. TIP: Lower heat and add a splash of water if mushrooms begin to brown too quickly. • Add onion and another drizzle of oil; season with salt and pepper. Cook, stirring, until veggies are browned and tender, 5-7 minutes. • Stir in stock concentrate and 2 TBSP water; cook until water has evaporated and mixture is jammy. • Turn off heat; remove from pan and set aside. Wash out pan.

• Spread half the sourdough slices with mustard, then top with even layers of Swiss (tearing to fit if necessary), mushrooms and onion, and Monterey Jack. • Top with remaining sourdough slices to create sandwiches.

• Melt 1 TBSP butter in pan used for mushrooms and onion over medium heat. (For 4 servings, work in batches or use a second pan, using 1 TBSP butter for each batch.) Add sandwiches and push around in pan until melted butter has absorbed. Cook until bread is golden brown and cheese is slightly melted, 4-6 minutes.

• Add another 1 TBSP butter to pan, then flip sandwiches and push around again until melted butter has absorbed. Cook until bread is golden brown and cheese melts, 4-6 minutes. TIP: If you have a heavy-bottomed pan, place on top of the sandwiches as they cook for a real panini experience! • Halve panini on a diagonal and divide between plates. Serve with potato wedges and horseradish aioli on the side for dipping.