Bring a large pot of water to a boil. Put salt into the water.
When the water is boiling, add in potatoes and allow to simmer on medium for 15-20 minutes until tender.
When potatoes are almost tender, add cauliflower into the boiling water. Allow to simmer 3–5 minutes until softened.
Drain water from potatoes and cauliflower and allow to cool for 5 minutes.
In a separate small pot, turn heat on medium. Add in butter and garlic. Sauté garlic until golden brown about 3 minutes. Then add in milk and cream. When this mixture is almost about to bubble, turn off heat.
Add cauliflower and potatoes into a blender. Then add in cream mixture. Add in grated aged white cheddar, Parmigiano Reggiano, and garlic salt. Blend on high until completely smooth but do not over-blend.
Serve while warm.
