Cook pasta to al dente, drain and set aside (do not overcook!)
In a large skillet or dutch oven, over medium heat, melt butter.
Add garlic and onion powder to butter. Stir for just under 1 minute, to allow the flavours to blossom.
Add the flour 1/2 tbsp at a time and stir/whisk into butter, ensuring minimal clumps remain.
Pour in the milk 1 cup at a time and stir/whisk well to work into butter/flour mix. Again, ensuring no clumps remain.
Add in nutritional yeast, cheese, mustard and salt. Keep stirring until most of the cheese has melted.
Remove from heat and add in pasta. Stir well and add additional sea salt if necessary.