Combine brown sugar, water, and cinnamon (if using) in a small saucepan over medium heat.

Stir until the sugar dissolves, then simmer without stirring for 3 to 4 minutes until the syrup lightly coats the back of a spoon.

Remove from heat, stir in vanilla extract if using, and keep warm on the lowest heat setting while you fry the fritters.

Peel the yam and grate it finely using a box grater or food processor.

Pile the grated yam onto a clean kitchen towel, wrap it tightly, and squeeze firmly over the sink until no more liquid drips out. The yam should feel almost powdery.

Transfer the squeezed yam to a mixing bowl. Add flour, beaten egg, salt, and cinnamon. Mix with a fork until a rough, cohesive batter forms. Do not overmix.

Pour oil into a 10-inch nonstick skillet or cast iron pan to a depth of about 1 cm. Heat over medium to 170 C / 340 F, checked with an instant-read thermometer.

Scoop heaped tablespoons of batter into the hot oil, leaving space between each one. Work in batches of 4 to 5 - do not crowd the pan.

Press each fritter flat immediately with the back of a spatula to about 1 cm thickness.

Fry for 3 to 4 minutes on the first side until the edges look golden and the center looks set, then flip and cook for another 2 to 3 minutes until deep golden on both sides.

Transfer fritters to a wire rack. Repeat with remaining batter, adjusting heat as needed to keep the oil at temperature.

Arrange the hot fritters on a serving plate or platter.

Spoon or pour the warm brown sugar syrup over the fritters while they are still hot so the syrup soaks slightly into the edges.

Serve immediately for the crispiest result.