Preheat the oven to 350 F. Line an 8×8 inch square pan with parchment paper on both sides (to make a + sign, this is for easier lifting).
Melt the butter and combine with the cookie crumbs. Press it into the bottom of the parchment lined pan, it doesn’t need to go up the sides, just the bottom. Use a measuring cup to tightly pack the crumbs into one layer.
Prep the lemon curd ingredients before the crust goes into the oven: set mesh sieve over heatproof bowl. Whisk together the sugar, lemon juice, eggs, yolks, zest, salt and starch in a pot. Set the pot over medium heat.
Set the crust in the oven for 10 minutes. While it’s baking, continue whisking the lemon curd as the sugar dissolves and the curd thickens. Once it covers the back of a spoon add the butter by dropping a tablespoon at a time, and whisking it in. Once all the butter is incorporated and you have a smooth, shiny thick curd, pour it through the mesh sieve.
Once the crust has baked for ten minutes, pour the lemon curd over it and return to the oven for about 10 minutes, until it has set (jiggle the pan to test it).
Let the curd cool at room temperature then in the fridge overnight.
To make the ganache: set the chocolate in a heatproof bowl and keep a wooden spoon or rubber spatula nearby. Warm the heavy cream in a small pot for a few minutes, until you see the heavy cream bubbling at the sides and it’s hot to touch. Pour it over the chocolate and give it a quick stir to coat all the chocolate. After 30 seconds, stir it until you have a smooth shiny ganache. Pour the ganache over the chilled lemon bars and let set in the fridge for 30 minutes.
Store the bars in the fridge. Serve cold!