Beer Battered Codwich Sliders

Ingredients

• 1 cup mayo
• 2 tablespoons capers, drained and chopped
• 2 tablespoons pickle relish
• 1 tablespoon fresh lemon juice
• 1 1/2 teaspoons white wine vinegar
• 1/2 teaspoon Worcestershire sauce
• Kosher salt and freshly ground black pepper
• 1 1/2 cups red cabbage, sliced thin
• 1/4 cup fresh parsley leaves, chopped
• 1 medium bulb fennel, trimmed and thinly sliced, save fronds for garnish
• 2 tablespoons fresh lemon juice (from about 1 lemon)
• 2 tablespoons Dijon mustard
• 1/2 cup extra-virgin olive oil
• Kosher salt and freshly ground black pepper
• 6 cups peanut oil, for frying
• 2 cups plus 1/2 cup flour
• 1 teaspoon baking powder
• 1/4 teaspoon table salt
• One 12-ounce bottle good beer (Irish stout preferred)
• 1 egg, lightly beaten
• 1 pound cod fillet, cut into pieces the length of the buns
• Kosher salt and freshly ground black pepper
• 8 parker house rolls, buttered and griddled until toasted