It should be fairly simple:
It looks like chocolate cake with
a layer of buttercream as the white filling,
some purple (possibly black and purple mix) sanding sugar/sugar crystal sprinkles on the outside of the cake portion.
Then the top either is rock candy (sugar that has been allowed to form big crystals with purple coloring), or even easier - a silicone mold on etsy "Silicone Gem Soap Mold" so I'm sure they're around elsewhere with hard candy (made from sugar with purple and black coloring) done well to get the mix of amethyst shades placed on top.
It's not nuts ;p The sanding sugar is just small sugar, it can be tinted and flavored, it's obvious there's something pressed on the outside of the cake (think of it as easy as putting colored sugar sprinkles on Christmas cookies - it's for looks, not taste as it makes things too sweet and...crunchy-ish.
The 'amethyst' is some sort of hard candy. Rock candy (lots and lots of sugar and some color dissolved in boiling water then allowed to re-form crystals) usually has small crystals but this cake looks fairly small due to the size of the fork.
Food safe silicone mold can be used for chocolate or candy and that one on etsy looks pretty spot on for the top of this image. Make that same liquid sugar but heat it until it's at the hard crack stage (basically all the water is gone at this stage and any candy formed will be hard, like toffee, lollypops, etc. - it's a stage on a candy thermometer) pour it in the mold, let it cool, pop it out and put it on top.
This is pretty, not tasty.
Seriously, if you can bake a box cake mix, and can manage not to burn yourself with molten sugar it would not take much to do this. Make/buy cake, icing, colored sugar - layer those, press sugar against the sides of the cake. Boil sugar and water until the thermometer reaches hard-crack. Pour into the silicone mold. Let it cool. Push it out of the mold and put it on top of the rest. Boom, pretty, crunchy, too sweet cake. Not, hard.
Not even for eating, it just looks amazing.
It looks like chocolate cake with
a layer of buttercream as the white filling,
some purple (possibly black and purple mix) sanding sugar/sugar crystal sprinkles on the outside of the cake portion.
Then the top either is rock candy (sugar that has been allowed to form big crystals with purple coloring), or even easier - a silicone mold on etsy "Silicone Gem Soap Mold" so I'm sure they're around elsewhere with hard candy (made from sugar with purple and black coloring) done well to get the mix of amethyst shades placed on top.
The 'amethyst' is some sort of hard candy. Rock candy (lots and lots of sugar and some color dissolved in boiling water then allowed to re-form crystals) usually has small crystals but this cake looks fairly small due to the size of the fork.
Food safe silicone mold can be used for chocolate or candy and that one on etsy looks pretty spot on for the top of this image. Make that same liquid sugar but heat it until it's at the hard crack stage (basically all the water is gone at this stage and any candy formed will be hard, like toffee, lollypops, etc. - it's a stage on a candy thermometer) pour it in the mold, let it cool, pop it out and put it on top.
This is pretty, not tasty.