Line an 8x8 baking pan with parchment paper. Set aside.

In a large mixing bowl combine the butter, syrup, brown sugar and granulated sugar. Heat on high in the microwave for 1 minute. Remove and stir and repeat cooking on high for another minute. Remove from the microwave and stir again. Cook for one more minute (for a total of 3) but watch the mixture closely as it may boil and bubble over if not watched.

Add the vanilla, cinnamon, cream of tartar, and salt. Stir until combined. Add the oats folding until incorporated. Add the flour in three portions taking care to mix well after each addition. If the mixture is still very wet and sticky, add more flour one tablespoon at a time.

Press the mixture into the prepared pan and refrigerate for an hour to set. Slice into desired size bars and drizzle with melted white chocolate if desired.