Start by preheating your oven to 350°F (175°C). While it's heating, grease your donut pan thoroughly to prevent sticking.

In a large mixing bowl, combine 1 cup of crushed Cinnamon Toast Crunch cereal with buttermilk. Give it a gentle stir and set aside to let the flavors meld.

In a separate bowl, whisk together your dry ingredients: flour, cinnamon, baking soda, and baking powder.

Return to your cereal mixture and add a lightly whisked egg, oil, maple syrup, vanilla, Greek yogurt, brown sugar, and melted butter. Stir until everything is well combined.

Gradually add your flour mixture to the wet ingredients, stirring gently until just combined. Be careful not to overmix.

Transfer your batter to a piping bag or use a spoon to fill each donut cavity about ¾ full.

Before baking, gently tap the pan on the counter to remove any air bubbles and even out the batter.

Bake for 10 minutes, or until the tops of the donuts spring back when lightly touched.

Allow the donuts to cool in the pan for 15-20 minutes before removing.

While cooling, prepare your glaze by mixing powdered sugar, milk, maple syrup, vanilla extract, and cinnamon until smooth.

Once cooled, dip the tops of your donuts in the glaze and immediately sprinkle with crushed Cinnamon Toast Crunch cereal.

Let the glaze set before serving and enjoying your homemade Cinnamon Sugar Toast Crunch Donuts!