To prepare the roasted plum tomatoes, preheat the oven to 475°F.
Spread ¼ cup of the oil on a rimmed nonstick baking sheet that is large enough to hold the tomatoes in one layer. Place the tomatoes, garlic, and thyme sprigs on the baking sheet, season with salt, and roll the tomato halves to coat them evenly with oil, leaving them round side up. Roast, turning the baking sheet once for even cooking, until the tomatoes are shriveled and slightly charred, 35 to 40 minutes. If any of the garlic overbrowns, remove it.
When the tomatoes are cool enough to handle, slip off the skins. Discard the thyme and store the tomatoes, with the pan liquid, in a covered container in the refrigerator for up to 1 week. You will have double the tomatoes you need to prepare the vinagrette; enjoy the extras in other salads or with grilled dishes.
To prepare the vinaigrette, place 8 roasted tomato halves, 2 tablespoons of the tomato liquid, the basil, and the vinegar in a food processor, and pulse a few times to blend. Add the remaining ½ cup olive oil and pulse a few more times; the consistency should be slightly chunky. Season with salt and pepper to taste.
To prepare the BLT salad, toss the lettuce and beefsteak tomatoes with the vinaigrette in a large bowl. Arrange on serving plates or in bowls, top each salad with 2 bacon strips, and serve.
• Add crumbled cheese (goat, feta, shredded cheddar).
• Substitute your favorite dressing.
• Use the roasted tomatoes and/or vinaigrette in other salads or to marinate chicken or mild white fish such as halibut or cod.