Bring a pot of water to boiling for the pasta. Cook the pasta until al dente and drain well so that you don't have excess cooking water which will dilute the flavor. While the pasta is cooking, melt the grapeseed oil and butter in a large saucepan over medium heat, and add the onion and garlic, cooking until translucent, being careful not to burn. Add the flour a little at a time to make a roux. Do this gradually because some batches of flour absorb more than others and you may not need as much. Add the bay leaves, and then incorporate the vegetable stock a little at a time to form a smooth sauce. Simmer for at least 10 minutes to allow the flour to "cook out," then remove the bay leaves. Add the heavy cream and Cheddar cheese, then season with salt and white pepper. Fold in as much pasta as you need to acquire the right consistency for macaroni and cheese. Transfer to a serving bowl and garnish with chopped chives.