Char half of the tomatoes over hot coals on the grill or over an open flame until well-blistered and tender. Hold in a nonreactive bowl. Dice the rest of the tomatoes and place in same bowl with chipotle peppers and tomato paste. Heat 1 ounce of the olive oil in a medium sauté pan until it shimmers. Add the garlic and onions and cook while stirring until golden brown.
Remove from heat and add to the tomatoes. With an immersion blender or a food processor, purée all ingredients to a smooth consistency. Pass through a fine sieve and discard the solids. Refrigerate the tomato mixture overnight.
To serve:
Stir mixture well and add kosher salt to taste. Ladle soup into 8 bowls and drizzle the rest of the olive oil over each bowl. Top with fresh ground pepper and serve immediately.