Step 1

1 Place a baking rack in the middle of the oven and preheat the oven to 350 degrees

Step 2

2 Bring a large pot of generously salted water to a boil

Step 3

3 Meanwhile, cut off the bottom quarter-inch of the leek, removing the root, and the dark green, fibrous parts of the leek (where it starts to unfurl) and discard, compost or save for vegetable broth

Step 4

4 Cut the remaining leek in half lengthwise

Step 5

5 Using just the white and light green parts, wash the leeks under running water, separating them to rinse in between the layers, until the water runs clear

Step 6

6 Thoroughly pat dry and thinly slice

Step 7

7 Separate the broccolini florets from the stalks and chop the florets into bite-size pieces

Step 8

8 Thinly slice the stalks

Step 9

9 In a large ovenproof skillet or fireproof casserole set over medium heat, melt the butter

Step 10

10 Add the leeks, broccolini stalks, garlic and thyme and cook, stirring frequently, until the vegetables are softened, about 15 minutes

Step 11

11 Stir in the flour, then slowly stir in the milk

Step 12

12 Cook, stirring frequently, until slightly thickened, 5 to 10 minutes

Step 13

13 Add the macaroni to the boiling water and cook for a minute or two less than the package instructions, until al dente; drain

Step 14

14 While the pasta is cooking, stir the Parmesan and all but a few tablespoons of the cheddar into the sauce and mix well

Step 15

15 Transfer to a blender (or use an immersion blender), add the spinach and puree until smooth

Step 16

16 (You may need to work in batches to avoid overcrowding the blender

Step 17

17 ) Stir in the 1/2 teaspoon salt and the pepper, taste, and add more, if needed

Step 18

18 Return the sauce to the skillet or casserole and stir in the pasta and broccolini florets, loosening with a splash of milk, if needed

Step 19

19 Sprinkle the remaining cheddar on top, along with the almonds

Step 20

20 Transfer to the oven and bake for about 30 minutes, or until golden and bubbling

Step 21

21 Serve hot