Mix the flour, cinnamon, and baking powder in a medium bowl. Set aside.
Melt the butter in a small saucepan over medium heat until it is halfway melted. Take it from the heat and stir until it is all melted. Set aside to cool.
Place the sugar in a big bowl and add the melted butter. Stir with a whisk for 10-15 seconds until combined.
Add in the egg and whisk for 10 seconds or until combined. Add the vanilla and stir.
Finally, add the flour mixture in 4 batches and mix until totally incorporated. You can use your spatula in the last batch to mix easily.
Cover the bowl with a plastic film and keep the mixture in the fridge for 10-15 minutes or until the dough becomes firm. ( Alternatively, you can bake them immediately, they won't spread too much but they wouldn't be as thick as the ones that you keep in the fridge.) The more you keep the dough in the fridge, the more deep flavors come out. At the same time preheat the oven to 325°F(165C°). Line baking sheet with parchment paper or silicone baking mat. Set aside.
Remove the dough from the fridge and make 40 gram balls. You can divide the mixture into 17 equal pieces as the dough makes 17 cookies.
Bake for 9 minutes or until the cookies are just slightly set. The cookies will be too soft to handle. Remove the cookies from the oven. Using a spoon, press the cookies to give their shape. Let them cool on the baking sheet for 15 minutes or until the cookies are firm enough.