*You can bake these up to 1 month ahead: Wrap the cooled baking pan in plastic wrap and freeze (no need to cut into them first). The baked bites can also be refrigerated, wrapped in plastic, for up to 2 days.
For the shortbread base:
- 190g (1 ½ cups) plain (all-purpose) flour
- 85g (¾ cup) icing (confectioners’) sugar
- ¼ teaspoon table salt
- 255g (12 tablespoons.) butter alternative, cold and cut into small pieces
- ½ teaspoon vanilla extract
For the Kahlua Chocolate Fudge layer:
- 450g (1 pound) plain (bittersweet chocolate) broken into squares
- 180ml (3/4 cup) almond milk
- 115g (8 tablespoons) butter alternative
- 4 eggs
- 130g (⅔ cup) granulated sugar
- 2 tablespoons Kahlúa
- 1 teaspoon vanilla extract
To make the shortbread base:
Heat the oven to 180℃ (350°F).
Line the bottom and sides of a 20x30cm (9×13-inch) baking pan with baking paper, allowing the paper to overhang to the pan to act as handles for removing the cookie later.
In a food processor, combine the flour, icing (confectioners’) sugar, salt, the cold butter pieces, and the vanilla over the flour and process, using short pulses, until the dough begins to form small clumps, 1 to 1-1/2 minutes. Turn the dough into the prepared pan. Using the bottom of a measuring cup, the back of a spoon or fingertips, press the dough into the pan in a smooth, even layer.
Bake until pale golden, 22 to 25 minutes.
Transfer the pan to a cooling rack and lower the oven temperature to 160℃ (325°F).
To make the Kahlua Chocolate fudge layer:
In a small saucepan over low heat (or in the microwave in a microwave-safe bowl)l, melt the chocolate, milk, and butter together. Whisk until smooth and set aside to cool slightly.
In the bowl of a food processor fitted with the mixing attachment (or in a stand mixer fitted with a paddle attachment or in a large mixing bowl, using a hand-held electric mixer) beat the eggs, sugar until lighter in color and frothy. Add the Kahlúa and vanilla and mix until combined.
With machine running, gradually add the chocolate mixture. until well blended, about 30 seconds.
Pour the chocolate mixture over the baked shortbread base. Bake until the sides are slightly puffed and a toothpick inserted near the center comes out wet and gooey but not liquid, 25 to 30 minutes. Transfer the pan to a rack.
When completely cool, cover with plastic and refrigerate until very cold, at least 12 hours or up to 2 days. To serve, using the baking paper as handles, lift the rectangle from the pan and set it on a cutting board. Tipping the rectangle, carefully peel away the paper. Using a hot knife, cut into bite-sized pieces.
Let sit at room temperature for about 5 minutes before serving.