For the gnocchi:
- 400g russet potatoes
- 70g “00” pasta flour
- 3g baking powder
- 6g salt
- 1 large egg yolk
- Salt, to cover the surface of a sheet tray
Preheat the oven to 185°C. Cover the surface of a baking tray with a bed of salt. Set the potatoes on top of the salt, then bake for 1.5 hours until tender.
Slice the potatoes lengthwise and scoop out the halves from the skin. Pass the potatoes through a ricer until smooth and fluffy.
Transfer the mashed potatoes into a large mixing bowl and add flour, salt, and baking powder, gently folding with a wooden spoon until just incorporated. Add the egg yolk, mixing until it becomes the texture of a soft dough. Be careful not to overwork or overmix the dough as it will activate the starches and result in a dense, tougher gnocchi.
Transfer the dough onto a floured work surface. Roll out the dough into a long 2.5cm thick rope. Cut into 4cm gnocchi. Place on a floured baking sheet, cover with cling film, and set aside at room temperature for 30-40 minutes to allow the gnocchi to prove and gently rise a bit.
Prepare an ice bath by filling a mixing bowl with ice water. Bring a large pot of salted water to a boil. Boil the gnocchi about 12-15 at a time (so the pot isn’t overcrowded), stirring occasionally, until they float (it takes only about 1 minute or so). Once they’re floating, continue to simmer for 1 minute. Transfer to the ice bath to stop cooking. Repeat this process with the remaining gnocchi. Store on a baking sheet (or similar) lined with a clean lint-free tea towel.
To make the sauce, bring the milk to a simmer over medium heat (do not fully boil), then remove from the heat. Melt the butter in a saucepan over medium heat, then stir in the flour with a wooden spoon. Cook for 3-5 minutes, stirring, making sure there are no lumps, until a thick glossy paste forms (this is known as a roux). Carefully pour in the hot milk and stir to combine. This sauce is known as a béchamel. Stir the Dijon, cream and both cheeses into the béchamel until combined. Cook for a further 2-3 minutes while stirring. Season with salt and pepper to taste.
To serve the dish, in a non-stick pan, melt 1 tbsp of butter over medium heat. Sear 8-10 gnocchi for 1-2 minutes on each side until golden.
Ladle a large spoonful of the warm sauce onto a plate. Place the seared gnocchi on top. Finish with a generous amount of shaved parmesan, freshly cracked black pepper, and fresh lemon zest on top.