Best Irish Nachos Recipe - How To Make Irish Nachos

Ingredients

• 2 to 3 lb. brisket
• 1/3 c. Dijon mustard
• 2 tbsp. light brown sugar
• 1 (12-oz.) bottle Guinness
• 4 lb. medium Yukon Gold potatoes, cut into 1/2"-thick rounds
• 2 tbsp. extra-virgin olive oil
• 1 tsp. dried oregano
• 1/2 tsp. garlic powder
• Kosher salt
• Freshly ground black pepper
• 1 c. shredded yellow cheddar, divided
• 1 c. shredded white cheddar, divided
• 1 (15-oz.) can black beans, rinsed, drained, divided
• 1/2 small red onion, thinly sliced, divided
• 1/2 c. sour cream
• 1 tbsp. store-bought horseradish
• Pickled jalapeños and sliced chives, for serving