Step 1

Put a large pot of well-salted water on to boil.

Step 2

Heat olive oil in a large frying pan over low heat. Add onion and cook gently for 5 minutes, or until onions begin to soften.

Step 3

Increase heat to medium, add sliced fennel, and sauté gently for additional 6-8 minutes or until fennel is tender and slightly caramelized. Add garlic and red pepper flakes. Continue to cook, stirring frequently, for another 1-2 minutes. Turn off heat.

Step 4

Once fennel is almost cooked, add pasta to boiling water and cook to al dente.

Step 5

Drain pasta (reserving 1/2 cup of cooking water) and toss with onion and fennel mixture in pan, adding pasta water if needed.

Step 6

Add kale pesto and combine.

Step 7

Top with parmesan cheese, if desired.