Preheat oven to 375°F. Prepare baking sheet with silpat (silicone baking mat) or parchment paper.
In large skillet over medium heat, sweat onions and garlic in canola oil until soft and translucent (no color). Remove from heat and transfer to plate. Cool in refrigerator.
In small mixing bowl, whisk together eggs and egg yolks. Add Grape Nuts, milk, horseradish and Worcestershire. Stir to incorporate. Allow to set for 10-15 minutes for Grape Nuts to soften.
In large mixing bowl, mix together ground beef and ground pork with hands until incorporated. Add cooled onion mixture, ketchup, salt, pepper, herbs and Grape Nuts mixture. Mix well.
To test for seasoning, make a small meat patty (2-inch diameter) and sauté in skillet. Allow to cool and taste for seasoning. If under-seasoned, add more salt and/or pepper.
Once combined, transfer the meatloaf mixture to the prepared baking sheet and firmly form into a brick shape, about 2 to 3-inches high by 5-inches wide. Meat should be compact, not loose. Bake at 375°F for 20 minutes.
Remove meatloaf from oven and brush the remaining ¼ cup ketchup over the top of the loaf. Return to oven and continue baking for 15-25 minutes more, until internal temperature reaches 160°F. Remove from oven and allow to rest for at least 10 minutes before serving. Sprinkle with fresh chopped parsley and chives.