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Preheat the oven to 350°F. Lightly grease three 8" square pans, or line each pan with a parchment sling. If you only have one 8" square pan, that’s OK; you can bake the layers one at a time.
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To make the cake: Break the almond paste into large chunks and place into a mixing bowl or the bowl of a stand mixer. Add the sugar and salt, and mix using an electric hand mixer or the flat beater attachment on a stand mixer until sandy. The almond paste will have broken down into smaller pieces and be uniform in size.
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Add the butter and almond extract. Beat until slightly fluffy and lightened in color, stopping to scrape down the sides of the bowl as needed.
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Add the eggs, one at a time, mixing until each is fully incorporated before adding the next.
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Add the flour and mix until smooth.
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Divide the batter into thirds: portion approximately 1 cup (235g) of batter in 2 medium bowls. Leave the remaining third in your mixing bowl.
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To one bowl, add 3 tablespoons (16g) of the cocoa powder and 2 teaspoons water. Mix until combined. This will be the darkest layer.
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To another bowl, add the remaining 1 tablespoon (5g) cocoa powder and 1 teaspoon water. Mix until combined. This will be the middle layer. Do not add anything to the batter remaining in your mixing bowl; this will be the lightest layer.
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Transfer each of the batters to one of the prepared pans and spread evenly (a small offset spatula is a helpful tool here); the layers will be thin. If you only have one 8" square pan, start by baking the lightest layer first while the other batters rest at room temperature, then bake the middle layer, then the darkest layer. There’s no need to wash the pan in between bakes — just be sure that the pan has cooled completely before baking the next layer.
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Bake the cake for 9 to 11 minutes, or until the cake springs back to the touch and looks dry in the center.
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Remove the cake from the oven and cool in the pan for 10 minutes before turning it out to cool completely on a rack. Be sure that all of the cake layers are completely cool before assembling.
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To assemble the chocolate cake bars: Spread 1/4 cup (85g) of the jam on top of the lightest layer of cake, spreading it all the way to the edges. Top with the middle layer of cake and apply firm pressure to sandwich the two layers together.
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Spread the remaining 1/4 cup (85g) jam over the top of the middle layer, spreading it all the way to the edges. Top with the darkest layer of cake and, again, apply firm pressure to sandwich all 3 layers together. Wrap tightly in plastic wrap.
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Place the wrapped bars in a 9" x 13" pan (or any pan larger than an 8" square), and place an 8" square pan on top. Place 4 to 6 heavy cans (or something of comparable weight) inside the 8" square pan to weigh it down, compressing the cake layers below. Refrigerate overnight with the heavy weights on top.
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To glaze the chocolate cake bars: Remove the bars from the refrigerator, unwrap, and place the lightest layer side down on a cutting board. Place the chocolate wafers in a microwave-safe bowl and heat in 20-second increments, at 50% power, until melted. (Alternatively, melt the chocolate in a small saucepan over low heat, stirring frequently.) Stir the chocolate until smooth.
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Spread the melted chocolate over the top of the darkest layer of cake, spreading it all the way to the edges. It’s OK if some chocolate drips down over the edges.
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Allow the chocolate to set either at room temperature or in the refrigerator. Once set, use a warm chef’s knife to trim the sides of the square (baker’s snack!) for a neat presentation, before cutting the remainder of the chocolate cake bars into pieces. Serve at room temperature.
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Storage information: Store any leftover chocolate cake bars in the refrigerator in an airtight container for up to 2 weeks; freeze for longer storage (see "tips," below). Allow the pieces to come to room temperature before serving.
