Position two racks in the oven, one in the middle, and one in the bottom, and preheat it to 170°F (75°C). Line two baking sheets with parchment paper.
In a saucepan, bring the maple syrup to a boil and cook until a candy thermometer indicates 250°F (120°C). Remove from the heat while you beat the egg whites.
In the bowl of a stand mixer, or in a large mixing bowl if you're using a hand mixer, beat the egg whites with the cream of tartar until soft peaks form. Slowly add the hot maple syrup to the egg whites, beating constantly, making sure the syrup never touches the whisk (it would create sugar crystals). Keep on beating for about 3 minutes, until stiff peaks form.
With a pastry bag fitted with a plain round tip, shape the mini-meringues on the lined baking sheets: Hold the tip close to the baking sheet, press down on the bag to create an inch-wide [2.5-cm-wide] base, then lift up a little, pressing more lightly, then stop and lift swiftly. This should create the classic “kisses” shape. Keep on piping the meringues, setting them about 1 inch (2-cm) apart (they will not expand). Sprinkle each meringue with a little maple sugar.
Place both baking sheets in the oven and let the meringues dry slowly for about 3 hours, switching the sheets halfway through. Depending on your oven and the temperature (whether it’s humid in your kitchen or not), it may take longer to dry the meringues. To check for doneness, try to lift a meringue from a baking sheet. If it comes off easily, it’s done. If it sticks, even a little, let them dry more. Once the meringues are done, turn the oven off, and leave the meringues in the oven for another hour.
The meringues will keep in an airtight container in the refrigerator for up to two weeks.