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.