Cream of tartar acidifies the syrup and helps break down the sucrose into glucose and fructose. The last 2 are the simple sugars that are utilized by bees. If you don't acidify the syrup, the bees will break down the sucrose on their own. I achieve the same by using vinegar.
You can add pollen or pollen substitute once the syrup cools down and starts to solidify. I usually just pat it on top.
If you are curious, here is my blog post (and printable recipe) for my candy board:
Fall Inspections: Bee candy boards and upper entrances
The post also has a link to a YouTube video that shows the process.