German-Style Fried Potatoes

INGREDIENTS

• 1/3 cup chopped fresh chives or green onions (green parts only)
• 1 tablespoon Dijon mustard
• 6 tablespoons lager beer, divided
• 3 tablespoons malt vinegar or white wine vinegar
• 4 1/2 tablespoons olive oil
• 6 tablespoons lard, rendered bacon fat, or olive oil, divided
• 4 pounds unpeeled medium-size red-skinned potatoes
• 2 1/2 cups finely chopped red onions, divided
• Coarse kosher salt