How to Make It
Preheat the oven to 400°. In a food processor, combine the pine nuts with the Parmigiano-Reggiano, Pecorino Romano, smashed garlic clove and 3/4 cup of the olive oil and pulse until smooth. Add the basil and pulse until finely chopped. Season the pesto with salt and pepper.
In a roasting pan, toss the Jerusalem artichokes with the parsnips, thyme sprigs, garlic head and the remaining 1/4 cup of olive oil. Season with salt and pepper. Roast the vegetables for 45 minutes, stirring occasionally, until tender and golden. Discard the garlic and thyme; stir in the vinegar.
Meanwhile, arrange the bread slices on a large baking sheet and toast in the oven until lightly browned, about 8 minutes. Spread the almonds in a pie plate and toast until golden, about 5 minutes.
Preheat the broiler and position a rack 6 inches from the heat. Spread each toast with a rounded tablespoon of the pesto. Top with the roasted vegetables and Fontina. Broil for about 1 minute, until the cheese is just melted. Sprinkle with the toasted almonds and serve right away.