Heat the oven to 400°F. Meanwhile, rub poblano chili lightly with oil, and grill directly over an open flame, using metal tongs to turn it until skin is blistered and charred. Transfer to a bowl, and cover; it will steam as it cools. When cool, peel, removing as much of the charred skin as you can. Make a lengthwise slit in the chili, remove the stem and seeds, and cut into a large dice.
FOR THE SALAD: Toss the squash, red pepper, and onion in a large bowl with 2 tablespoons olive oil, salt, and Ancho Chili and Chipotle Purees. Spread the vegetables on one or two baking sheets, and roast for 15 minutes. Use a spatula to loosen and turn vegetables, and roast until tender, about 15 minutes more. Set aside to cool. Lower the oven to 375°F.
Prepare the Fromage Blanc Custards. Combine all ingredients in a medium bowl, and whisk until smooth.
Lightly oil a baking dish or dishes. If using individual baking dishes, place them on an oiled baking sheet before filling. Toss the vegetable mixture with fire-roasted chili, cheeses, and herbs. Season to taste with salt. Filled the baking dish(es) with vegetable mixture and press firmly, leaving room at the top for custard. Pour custard over the top. Bake until golden, about 30 minutes for individual servings or 40 minutes for a single dish. Run a paring knife around the edges to loosen the gratin, and serve.