Preheat oven to 160 degrees celsius and brush an 8" sprigform tin with butter.
In a bowl, melt chocolate and butter in a bowl over a double boiler or in a microwave over 15 second intervals, once completely melted mix them properly so that they're combined. Set aside and let it cool down.
Next, separate the eggs. In another bowl, whisk egg yolks sugar, vanilla, instant coffee mixed in 2 tablespoons of water and salt until they're fluffy. Add in the chocolate mixture to this slowly until you have a smooth mixture.
Now whip your egg whites until they have tripled in size and are almost foamy, start adding these egg whites to the chocolate mixture little by little. Mix the fist batch properly before adding the next.
Add in the orange zest and juice, mix them in too. Pour them in the prepared tin and Bake for 40 mins at 160 degrees celsius.
Serve with some whipped cream or vanilla ice cream and some chocolate glaze.
Recipe by Sugar & Spice by Radhika at https://sugarnspicebyradhika.in/flourless-chocolate-orange-cake/