Adjust oven rack to middle position and heat oven to 350°F. Process tomatoes and onion in food processor until smooth and thoroughly pureed, about 15 seconds, scraping down bowl if necessary. Transfer mixture to liquid measuring cup; you should have 2 cups (if necessary, spoon off excess so that volume equals 2 cups). Remove ribs and seeds from jalapeños and discard; mince flesh and set aside.
Place rice in large fine-mesh strainer and rinse under cold running water until water runs clear, about 1½ minutes. Shake rice vigorously in strainer to remove all excess water.
Heat oil in heavy-bottomed ovensafe 12-inch straight-sided sauté pan or Dutch oven with tight-fitting lid over medium-high heat, 1 to 2 minutes. Drop 3 or 4 grains rice in oil; if grains sizzle, oil is ready. Add rice and fry, stirring frequently, until rice is light golden and translucent, 6 to 8 minutes. Reduce heat to medium, add garlic and seeded minced jalapeños; cook, stirring constantly, until fragrant, about 1½ minutes. Stir in pureed tomatoes and onions, chicken broth, tomato paste, and salt; increase heat to medium-high and bring to boil. Cover pan and transfer to oven; bake until liquid is absorbed and rice is tender, 30 to 35 minutes, stirring well after 15 minutes.
Stir in cilantro. Serve immediately.