Set the oven to broil. Add the pasta to a pot of boiling salted water and cook until al dente, 8 to 10 minutes.
Pulse the crackers in a food processor to a coarse consistency. Mix with the chives and parsley.
Whisk the butter and flour in a medium saucepot over medium-high heat until fully incorporated and bubbly. Add the milk and bring to a simmer, whisking the entire time. Whisk in the cheeses, a little at a time, until thoroughly combined. Add the heavy cream and season with salt and pepper.
Strain the pasta and mix with the cheesy sauce. Spoon into oven-safe baking vessels and top with the crumb crust. Place under the broiler until lightly toasted and bubbling, 3 to 5 minutes. Watch carefully so the mac doesn't burn.