Preheat oven to 350.
Place cracker crumbs and rosemary in small bowl. Set aside.
Melt 1 stick of butter in medium saucepan over medium heat. Continue melting until the butter starts to get foamy. Continue cooking, keeping close watch, until brown specks start to form and you smell a nutty aroma. Remove from heat. *See Recipe Notes
Pour half of the brown butter (1/4 cup) into the bowl with the crushed crackers. Mix until well combined, set aside.
To the remaining 1/4 cup of brown butter, add 2 TBS Bourbon Whiskey. Set aside.
In large saucepan over medium-low heat, melt the remaining 3 TBS of butter. Add diced onions, 1/2 tsp salt and sugar. Stir to combine.
Cook, stirring occasionally, until onions are caramelized and golden, about 10-15 minutes.
Add in garlic, cook 1 minute.
Add in flour, whisking constantly for 2-3 minutes until slightly browned.
Add in brown butter/bourbon mixture. Whisk for 1 minute longer.
Add in Milk and Half & Half, stirring often until slightly thickened, about 5 minutes (mixture will be bubbling).
Stir in pumpkin, cheeses (cheddar, American, Asiago, & cream cheese), black pepper, remaining 1/2 tsp salt, mustard, sage, cinnamon, nutmeg, and allspice. Stir until melted and smooth. Set aside.
Bring large pan of water to boil, add pasta and cook according to pasta instructions. Drain.
Add cooked pasta to cheese mixture. Stir to combine.
Pour into large 13"x9" baking dish, spreading out evenly.
Sprinkle cracker crumb mixture on top, spreading evenly.
Bake at 350 for 20 minutes, until top is golden and cheeses are bubbly.
Let cool 5-10 minutes before serving.