Add all pot roast ingredients to slow cooker. Secure lid and cook on low for 8 hours.
In the last 30 minutes of roast cook time, start water boiling for potatoes.
Add potatoes to boiling water and cook for 20 minutes.
Add corn ingredients to saucepan and cook on medium-low until ready to serve.
Drain potatoes and transfer to bowl. Add remaining potato ingredients and blitz with immersion blender until smooth.
Remove pot roast from slow cooker (reserve juices) and let rest on cutting board while making gravy.
In a saute pan over medium-high heat, melt butter. Whisk in flour and cook for 3 minutes. Ladle juices from slow cooker into pan and continue to whisk. Reduce heat to medium-low.
Use a fork to pull apart pot roast.
Build a bowl - start with a portion of potatoes and ladle gravy over top. Add potion of corn to side of bowl. Lay pieces of roast down center of bowl and ladle additional gravy over top. Garnish with parsley, if desired.