For a more refined version of this soup, puree it in a blender until smooth. Slideshow: More Warming Soup Recipes
In a large heavy pot, heat the oil over medium high heat until hot. Stir in the onions, garlic, and 1/2 teaspoon each salt and pepper into the fat in the pot and cook, stirring occasionally, until golden, 6 to 8 minutes. Stir in the carrots, celery, stock, and split peas and bring to a simmer. Cook, stirring occasionally, until the split peas are very soft and falling apart, about 1 1/2 hours.