Use a large glass bowl that is large enough to accommodate all ingredients and still allow for mixture to expand, as it will boil up quite a bit during the cooking process.
Mix together dry ingredients, including sugars, in glass bowl. Add corn syrup and sweetened condensed milk and stir to combine. Add butter. Microwave on High in 2 minute increments, stirring every 2 minutes.
After 8 minutes, begin stirring every one minute and checking temperature. Continue this process until temperature reaches 245-250° F.
Stir well and pour into parchment lined 13 X 9 baking pan.
Cool at room temperature for at least 1 hour before cutting into squares with a pizza roller.
Note – cooking time is based on a 1000 gram batch and will need to be adjusted for larger or smaller batch sizes