Step 1

Place 1 stick unsalted butter in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Let sit at room temperature until softened, about 1 hour.

Step 2

Arrange a rack in the center of the oven and heat the oven to 350°F. Line an 8-inch square baking pan with a parchment paper sling that covers the bottom and hangs over two sides.

Step 3

Place 2 cups all-purpose flour, 2 teaspoons ground cinnamon, 2 teaspoons ground ginger, 1 teaspoon kosher salt, 1/2 teaspoon baking soda, and 1/2 teaspoon baking powder in a medium bowl and whisk to combine.

Step 4

Coarsely chop 1/2 cup almonds and 1/2 cup hazelnuts if needed. Finely chop 1/4 cup crystallized ginger if using.

Step 5

Add 1 cup packed dark brown sugar to the bowl of butter. Beat with the paddle attachment on medium speed until creamy, about 2 minutes. Add 1/4 cup honey and 1 large egg and beat until smooth. Add the flour mixture and beat on the lowest speed just until incorporated. Add the almonds, hazelnuts, ginger, and 1/2 cup raisins, and beat on the lowest speed until fully incorporated. Transfer to the baking pan, pressing the dough into an even layer with damp hands to avoid sticking.

Step 6

Bake until the top is set, dry to the touch, and golden-brown, 25 to 30 minutes. Let the lebkuchen cool in the pan for 15 minutes. Remove the slab to a wire rack and let cool completely, at least 1 hour.

Step 7

Place 1/2 cup semi-sweet chocolate chips and 1 tablespoon unsalted butter in a small microwave-safe bowl. Microwave in 30-second intervals, stirring between each interval, until melted, 1 to 2 minutes total. Stir until smooth.

Step 8

Spread the melted chocolate over the lebkuchen, smoothing the top with a small offset spatula or the back of a spoon. Refrigerate until firm, about 20 minutes.

Step 9

Place 2 tablespoons milk chocolate chips, if using, in a small heatproof bowl. Microwave in 30-second intervals until melted, 30 seconds to 1 minute total. Use a spoon, fork, or a small piping bag to drizzle the milk chocolate over the lebkuchen. Refrigerate until firm, about 10 minutes, before cutting into small bars or squares.