Prepare water to boil the pasta. Bring plenty of water to a boil. (You can turn off the heat once it boils...)

Blanch the spinach in salted water and cut it into bite-sized pieces.

Turn off the heat and add the white sauce. Fill the empty can with milk and pour it, along with any remaining sauce, into the pan.

Reignite the heat and simmer the sauce over low to medium heat until it thickens. Adjust the taste with salt and pepper, add the spinach, and once it looks creamy, it's ready.

Cook the pasta. Depending on your preference, I usually cook it about 1 minute less than the standard time.

Transfer the cooked pasta into the white sauce using tongs or chopsticks. Add 2-3 spoonfuls of pasta cooking water and mix.