
2 cups all-purpose flour
¾ cup granulated sugar
2 teaspoons baking powder
½ teaspoon salt
2 large eggs
½ cup milk
½ teaspoon vanilla extract
¾ cup unsalted butter, melted and cooled slightly
*For paper liners, use either purchased paper baking cups or 4×4-inch pieces of parchment paper.
For streusel topping, in a food processor, place ¼ cup all-purpose flour; 2½ tablespoons cold unsalted butter, cut up; and 2 tablespoons granulated sugar. Cover and pulse until mixture is coarse. Add 3 tablespoons walnut pieces; cover and pulse until walnuts are coarsely chopped. Stir in 2 tablespoons finely chopped crystallized ginger; set aside. Prepare batter for Basic Muffins as directed. Fold 1 cup chopped fresh cranberries, ⅓ cup walnut pieces and 1½ teaspoons orange zest into batter. Spoon batter into prepared muffin cups; sprinkle with streusel topping. Bake as directed.
Bring about 4 cups water to a boil in a medium saucepan; remove from heat. Stir in 2 cups tightly packed baby spinach just until wilted; drain and squeeze dry. Coarsely chop spinach and cool. Prepare batter for Basic Muffins as directed, except omit the vanilla extract. Fold chopped spinach, ¾ cup shredded smoked Gouda cheese, 6 slices chopped crisp-cooked bacon and 1 tablespoon finely chopped fresh chives into batter. Spoon batter into prepared muffin cups; top with an additional ¼ cup shredded smoked Gouda cheese. Bake as directed.
Prepare batter for Basic Muffins as directed, except reduce flour to 1¾ cups and add 3 tablespoons unsweetened Dutch-process cocoa powder to the flour mixture. Fold ¾ cup chopped banana into batter. Spoon half of the batter into prepared muffin cups. Spoon about 1½ teaspoons chocolate–hazelnut spread into each muffin cup; top with remaining batter. Top batter in each cup with some of 2 chopped 1.55–ounce milk chocolate candy bars and some of ¼ cup chopped hazelnuts. Lightly sprinkle with sea salt flakes, if desired. Bake as directed.