Over medium heat, melt butter in large sauté pan. Add mushrooms, asparagus and cherry tomatoes. Salt and pepper. Cook 3-4 minutes until softened.
Add shallot, garlic and red pepper flakes. Cook 2 minutes until fragrant.
Whisk flour into cream until no lumps appear. Add cream mixture and 1/2 cup prepared pesto into pan. Stir until blended.
Add parmesan and asiago cheeses. Stir until melted. Add salt to taste.
Heat for additional 5 minutes to thicken and reduce, stirring frequently (do not boil).
Prepare tortellini according to package instructions.
Toss pasta in sauce. Top with sliced steak and serve.