Crisp Bacon Bits: Place bacon on a baking sheet lined with parchment paper. Place it on the middle rack of a preheated 400°F oven. Bake bacon until crispy and golden-brown. Set a timer for roughly 18 - 20 minutes. Place them on a paper towel to absorb the excess fat. Cut into bacon bits.
Pressure Cook Elbow Macaroni: Add 16 oz (454g) elbow macaroni, 4 cups (1L) cold water, and a pinch of kosher salt in Instant Pot. Close the lid and pressure cook at High Pressure for 4 minutes + Gradual Quick Release. Open lid carefully.*Pro Tip: There is a slight chance that a tiny amount of foam will come out with the steam. Have a towel handy just in case.
Prepare Crispy Breadcrumbs: While the macaroni is pressure cooking, heat a skillet over medium heat. Add 1 tbsp (15g) unsalted butter, 1 tbsp (15ml) olive oil, and ½ cup (31g) panko breadcrumbs to the skillet. Toast the breadcrumbs until golden brown. Taste and add kosher salt for seasoning.
Mix Wet Ingredients: In a medium mixing bowl, beat 2 large eggs and mix in 1 tsp (2g) ground mustard, 1 tsp (5ml) Sriracha, and 12 oz (355ml) evaporated milk. Mix well.
Make Mac & Cheese: Keep the heat on low or medium-low (Instant Pot: use the keep warm function). Give it a quick stir. If there is excess liquid in the pot, drain if necessary. Place 4 tbsp (60g) unsalted butter into the pressure cooked macaroni. Mix well with a silicone spatula and let the butter melt.
Pour in the wet ingredients and mix well. Add in the grated cheese 1/3 portion at a time and stir constantly until the cheese fully melt.
If the mac and cheese are too runny, turn the heat to medium (Instant Pot: Use Sauté Less function - Click cancel, Sauté and Adjust button twice) to reduce it down.
Taste & Season: Taste and season with kosher salt and ground black pepper (will probably need quite a few pinches of kosher salt to brighten the dish).
Serve: Generously sprinkle crispy breadcrumb, bacon bits, then scallion over a bowl of macaroni & cheese. Serve immediately & enjoy~