Measure out your 4 cups of Cheerios and put them in a really big bowl.
In a small saucepan over medium heat, or in a microwave-safe bowl, melt your 1/4 cup of butter. If using the microwave, heat in 30-second intervals, stirring in between, until fully melted.
Once the butter is melted, remove it from the heat (or microwave). Stir in the 1/4 cup of white sugar and the 1 tsp of ground cinnamon. Stir it really well until the sugar starts to dissolve a bit and the cinnamon is fully incorporated.
Now, stir in the 1/4 tsp of vanilla extract. Give it one more quick stir to make sure everything is mixed.
Immediately pour this warm buttery, sugary, cinnamon-vanilla mixture all over the Cheerios in the big bowl.
Grab a spoon or a rubber spatula and gently but quickly start stirring and tossing the cereal. You want to get every single Cheerio coated in that delicious glaze. Keep stirring until they look nicely coated.
Now comes the hardest part: letting them cool slightly! Spread the coated Cheerios out on a baking sheet lined with parchment paper or wax paper, or just on a plate. This helps them cool and get that lovely crispy texture.
Once they've cooled for about 5-10 minutes, dig in! They'll be slightly sticky, wonderfully crunchy, and taste just like little bites of cinnamon-sugar heaven.