Preheat the oven to 200 C/400 F. Grease and line a 12 count muffin tin with muffin liners and set aside.: The kitchen will fill with warm air as the oven approaches 200 C , and you want that consistent heat for even rise, so let the oven fully reach temperature before baking. Lining the tin prevents sticking and helps with easy removal, while greasing under liners adds insurance against stubborn bottoms. A common mistake is not preheating long enough, which can cause flat muffins with poor oven spring. You should hear the quiet hum of the oven settling and see a stable temperature on the dial before you open the door to load the tin.
In a large mixing bowl, add all the dry ingredients and mix well. Add the wet ingredients, except for the blueberries, and mix until well combined. Fold in the blueberries.: As you stir the all purpose flour , sugar free sweetener , baking powder , salt , and cinnamon , you will notice the dry mix looks uniform and slightly aromatic from the spice. Adding the wet applesauce and milk creates a batter that should be thick but pourable, with streaks disappearing as you fold. Folding in the blueberries at the end prevents them from breaking and bleeding into the batter. If you overmix at this stage you can develop gluten and end up with chewier muffins, so stop once the ingredients are just incorporated.
Evenly distribute the muffin mixture amongst the 12 muffin liners and bake in the oven for 25-30 minutes, or until a skewer comes out clean.: Spoon or scoop the batter into the prepared liners so each cup is nearly full but not overflowing, which encourages the classic domed top during baking. As they bake you will smell the cinnamon and notice the tops turning faintly golden. Use the skewer test in the center of a muffin to check doneness, and resist opening the oven in the first 15 minutes to avoid collapse. Baking too long dries the crumb, while too short leaves a gummy center, so aim for that clean skewer with a few moist crumbs attached.
Once cooked, remove from the oven and allow to cool in the muffin tin for 5 minutes, before transferring to a wire rack to cool completely.: Letting the muffins rest in the tin allows steam to redistribute and the internal crumb to set, which reduces tearing when you remove them. The 5 minute pause will feel impatient, but the texture benefits markedly. Transfer to a wire rack for full cooling so air circulates and tops do not steam and soften. A common misstep is leaving them on a hot pan where residual heat continues cooking and can dry them out, so move them promptly after that brief rest.
