Place the beef broth in a medium saucepan, bring to a boil, then reduce heat to a low simmer.
In a large pan with at least 2 inch (5 centimeter) sides, melt 2 tablespoons (28 grams) butter and the olive oil over medium low heat.
Add the onion and cook, stirring occasionally, until softened and translucent.
Toss in the penne until thoroughly covered in the butter and oil with a shiny appearance.
Pour in about 1/2 cup (120 milliliters) of the hot broth and constantly stir the pasta until the liquid has fully absorbed.
Add in another 1/2 cup (120 milliliters) broth, stirring until absorbed. Continue adding broth and stirring until absorbed before pouring in more.
Sprinkle the saffron over the last 1/2 cup (120 milliliters) broth in the saucepan and let it sit while you are stirring in the previous 1/2 cup (120 milliliters) of broth.
To finish, stir in the saffron-infused last 1/2 cup (120 milliliters) of broth until the pasta is al dente, just tender, and the liquid has mostly absorbed, leaving behind just enough to make a light sauce. Remove from heat.
Stir in the last 1 tablespoon (14 grams) butter, the grated Parmesan cheese, and black pepper.
Adjust seasonings to taste, adding salt if needed.
Divide among serving bowls. Top with more Parmesan if desired and serve immediately.