Shred both hard cheeses. Then set out the cream cheese to soften.: The room temperature creaminess you are aiming for should feel slightly yielding when pressed, and freshly shredded cheddar and smoked gouda will smell bright and savory, releasing dairy aromas that promise a rich sauce. Doing this ahead prevents long melt times and minimizes graininess, because cold cheese can clump when introduced to warm liquid. One common mistake here is skipping the softening step, which can lead to uneven pockets of unincorporated cream cheese, so plan a few minutes to let it come to room temperature.
Place a 6 quart pot of heavily salted water on the stovetop. Set on high heat and bring to a boil. Drop the pasta into the boiling water. Stir well and cook according to package instructions. Usually 6-9 minutes for al dente. DO NOT overcook the pasta; it should still be slightly firm. Then scoop out 1 cup of pasta water for later use, and drain the pasta in a large colander.: When the water hits a rolling boil and you add salt it should smell slightly metallic and sea like, which seasons the macaroni from the inside out. As the macaroni cooks you will see it swell and become more translucent at the edges, and testing a piece at around the lower end of the time range will help you catch it al dente, with a tender outside and a faintly firm center. Reserving a cup of pasta water before draining is crucial because its starch helps the cheese sauce cling and smooth out if it tightens up. A typical slip up is forgetting to salt the water, resulting in bland pasta, so don’t skip that step.
Meanwhile, set another 4-6 quart pot over medium heat for the cheese sauce. Add 3 tablespoons butter to the pot, then whisk in 2 tablespoons flour. Continue to whisk for 2-3 minutes until the roux mixture is golden in color. (This ensures even thickening without a grainy texture. If the roux is too light, the texture won’t be completely silky.): As you melt the butter , it will spread a nutty scent, and once you stir in the flour , the mixture should look glossy, thickening slightly as you whisk. Cooking the roux long enough eliminates any raw flour taste and primes it to evenly thicken the sauce. Watch closely because if the roux darkens too far it can impart a toasty flavor you may not want; a pale golden hue is ideal. If you notice lumps forming early, the heat is likely too high, so reduce it and whisk steadily.
Whisk the half & half into the roux, stirring until there are no clumps. Then add the cream cheese and shredded cheese. Stir to melt the cheeses. Add the salt, pepper, and garlic powder. Lower the temperature to make sure the cheese sauce doesn't boil.: Pouring warmer dairy into the roux produces a smooth, velvety base that will thicken as it gently simmers, and the aroma will become rich and slightly sweet. When you add the softened cream cheese it should dissolve almost immediately into the warm base, enriching the sauce, while the shredded cheddar and smoked gouda will gradually melt into a glossy, cohesive sauce. The surface might shimmer and emit a mouthwatering cheesy fragrance. Avoid boiling once the cheeses are added, because high heat can make the sauce separate and grainy; if that happens, remove from heat and whisk in a splash of reserved pasta water to bring it back together.
Pour the drained pasta into the cheese sauce and stir to coat. Then stir in the shrimp. Stir and cook the shrimp in the cheese sauce until all the shrimp are pink, 4-5 minutes. Add some of the pasta water if needed to loosen the cheese sauce.: As you fold the warm macaroni into the sauce the pan will release a comforting aroma and you should see each piece lacquered with cheese. Adding the raw, cleaned shrimp at this point lets them finish cooking gently in the sauce, absorbing flavor while releasing a faint briny perfume. Cook just until the shrimp turn fully pink and opaque, and you may hear a soft simmering sound, with tiny bubbles along the edge. Overcooking makes shrimp rubbery, so stop when they are firm but tender. If the sauce seems tight or clumpy, a splash of the reserved pasta water will loosen it and revive the glossy texture.
If you like creamy mac and cheese with a smooth silky consistent texture, you are done! The sauce does thicken a little as it cools, so if you want the sauce a little saucier, stir in 1/2 cup of the reserved pasta water. Serve warm with a sprinkle of parsley.: At the finish the casserole should look glossy and coating, with pink shrimp nestled among saucy macaroni . A final addition of reserved pasta water can adjust sauciness to your preference and will make the sauce shine. Garnish with chopped parsley for a bright herbal scent and a pop of color. The major pitfall here is letting the finished dish sit too long on high heat, which can thicken the sauce beyond repair, so serve promptly for the best texture.
