In a medium saucepan, combine the milk, butter and garlic and bring to a boil over high heat. Reduce the heat to moderately low and gradually whisk in the chickpea flour until smooth. Stir constantly with a rubber spatula until the mixture thickens, about 2 minutes. Season with salt and pepper.
Scrape the mixture into a nonstick 9-by-13-inch rimmed baking sheet or baking dish that has been lightly sprayed with vegetable oil spray; spread into a 1/4-inch layer. Cover with parchment paper and refrigerate until firm, 2 to 3 hours.
Pour 1 inch of canola oil into a wide skillet and heat it to 350°, or until a piece of bread bubbles rapidly when added to the hot oil. Meanwhile, cut the chickpea mixture into 2-inch squares. Fry the squares in batches until golden brown, about 1 minute per side. Transfer the squares to a rack lined with paper towels to drain, then keep them warm in a low oven while you fry the rest.
In a bowl, mix the sage and Parmesan cheese. Toss the fries in the cheese and sage mixture until coated; serve warm.
The recipe can be prepared through Step 3; refrigerate overnight. Recrisp the fries in a 350° oven. Toss with the sage and Parmesan before serving.
Chickpea flour is available at Indian markets and health food stores.