Biscuit base

1. Set a heatproof bowl over gently simmering water, making sure the bottom of the bowl does not touch the water.
2. Add the butter, sugar, and cocoa powder and stir until smooth. Gradually whisk in the beaten egg and continue cooking for about 2–3 minutes, stirring, until the mixture thickens slightly.
3. Remove from the heat. Stir in the crushed digestive biscuits, coconut, and chopped almonds until everything is evenly coated.
4. Press firmly into the prepared pan, getting the surface as level as possible. Refrigerate for about 10–15 minutes, or until firm.

Corn-free custard filling

1. Beat the softened butter until smooth and fluffy.
2. Beat in the heavy cream, dry milk, vanilla, salt, and optional turmeric.
3. Gradually add the powdered sugar and beat until light, smooth, and fluffy.
4. Spread evenly over the chilled biscuit layer.
5. Refrigerate for 30–45 minutes. I’d give this layer considerably longer than the 10 minutes in the original recipe because our filling is softer and creamier than a custard-powder buttercream. You want it quite firm before adding warm chocolate.
6. For homemade corn-free powdered sugar: pulverize 240 g granulated sugar + 2 tsp tapioca starch or potato starch in a high-speed blender until very fine and powdery.

Chocolate topping

1. Melt the chocolate and butter together gently, either over a double boiler or in short microwave bursts, stirring frequently until completely smooth.
2. Let it cool for a few minutes — warm and pourable, but not hot. That will help prevent it from melting the custard layer underneath.
3. Pour over the chilled custard filling and spread quickly into an even layer.
4. Refrigerate until completely firm, about 2 hours.

Cutting

1. Lift the slab from the pan using the parchment. For cleaner cuts, let it sit at room temperature for about 10 minutes before slicing.
2. Use a large sharp knife warmed under hot water and wiped dry between cuts. Cut into 16 squares.
3. One small tweak I particularly like here
4. Because the original base is quite substantial — 200 g biscuit + 100 g coconut + 50 g almonds — I think our 1/2-cup-butter custard batch is about right. It should give you that visually distinct creamy middle layer without overwhelming the chocolate/coconut base.
5. And this version should still look very much like the Hebridean Baker’s bar in your photo, just with our corn-free custard layer instead of commercial custard powder.