Preheat your oven to 350°F (175°C) and line a 9x13 inch baking pan with parchment paper.
In a medium saucepan over low heat, melt the butter (or vegan butter) until just melted. Remove from heat and let cool slightly.
In a large mixing bowl, combine the melted butter, light corn syrup, light brown sugar, granulated sugar, and vanilla extract. Whisk until smooth.
Add the ground cinnamon, cream of tartar, optional salt, quick cook oats, and flour to the wet mixture. Stir until thoroughly combined.
Pour the granola mixture into the prepared baking pan, spreading it evenly and pressing down firmly.
Bake for 20-25 minutes, or until the edges are golden brown. Keep an eye on them to avoid over-baking.
Once baked, remove from oven and let cool in the pan for about 10 minutes. Lift out using parchment paper and cool completely on a wire rack before cutting.
If desired, melt the white chocolate chips and drizzle over the cooled granola bars.
