Melt 4 tablespoons butter in a pot. Once melted add 4 tablespoons of flour. ( A Roux is traditionally equal parts flour to fat (butter) )
Cook for one minute. Next start adding the whole milk. Start off slowly making sure to incorporate the milk well. The consistency will tighten up. Once this starts to happen add in a little bit more whole milk. Repeat till the texture of the sauces is a little bit lose. The addition of the cheese will tighten the sauce up quickly.
Add cheese and stir until smooth. Add cheese sauce to the drained pasta and combine.
Lastly, pour the mac and cheese into a casserole dish lined with parchment paper ( easy removal ) or whatever you have that will create enough depth to make slider-shaped cuts later.
Cool the mac and cheese for 15 minutes, then refrigerate for one hour.
Cut the mac and cheese to the size that will fit the slider buns you bought.