1. Prep ingredients
Bring a medium saucepan of salted water to the boil for the pasta. Thinly slice the spring onion. Finely grate the parmesan (see Kitchen notes). Juice the lemon. Separate the smoked salmon slices, then coarsely tear into pieces.
2. Cook pasta
Cook the pasta in the pan of boiling water for 11 mins or until al dente. Drain.
3. Make sauce
Meanwhile, melt 20g butter in a medium deep frypan over medium heat. Add 1 tbs plain flour and cook, stirring, for 2-3 mins until golden (see Kitchen notes). Gradually add 60ml (¼ cup) milk and 125ml (½ cup) water, whisking constantly, and cook for 4 mins or until smooth and thickened. Season with salt and pepper.
4. Add pasta
Add the spring onion and half the parmesan to the sauce and stir to combine. Remove the pan from the heat. Add the spinach, pasta, smoked salmon and 1½ tbs lemon juice and toss until combined and the spinach is wilted. Taste, then season with salt and pepper.
5. Serve up
Divide the pasta among bowls, scatter over the remaining parmesan and drizzle with any remaining lemon juice, if desired. Enjoy!
6. Kitchen notes
If you like the rustic look in our photo, finely grate half the cheese, then use a vegetable peeler to shave the remainder, to serve. ~ It's important that you cook the flour until it turns golden, so the finished sauce doesn't taste of raw flour.