Line a 9x13 inch baking pan with parchment paper and set aside. Get out a large bowl and place the 7 cups of Cheerios in it.
Scoop the honey in a medium size sauce pan. Over medium-high heat, heat the honey until it reaches 265°F. (hard ball stage) You can also test this in water, drop a bit of the honey into cold water and if it forms a hard ball that can still be squished, it's ready.
Remove from the heat and instantly stir in the peanut butter, then stir in the vanilla.
Pour over the dry cereal in the large bowl and stir until the cereal is completely coated.
Turn out into the prepared pan, pressing down on the cereal to form a firm bar.
Let cool at room temperature until set. Do not refrigerate. Keep in a closed container at room temperature for up to 7 days.