Step 1

In a large saucepan, melt butter over medium-high heat

Step 2

Once the butter has melted, whisk in flour and cook until it begins to smell nutty and fragrant, about 45-60 seconds

Step 3

Whisk in milk and stock, and continue whisking vigorously until flour and butter have dissolved

Step 4

Bring to sauce to a bubble and thicken, about 3-4 minutes

Step 5

Once sauce is thick, remove from heat and mix in mustard and cheddar cheese

Step 6

Stir until cheese is completely melted