Bring a large pot of salted water to a boil. Boil the pasta shells according to the package until al dente. Add broccoli to boiling water during the last three minutes of boiling. Drain pasta reserving one cup pasta water.
When pasta is almost done boiling, in a separate pot, begin making sauce. Melt butter and add flour, salt, mustard powder, turmeric, garlic powder and pepper whisking together until paste forms. Add milk and whisk until combined. Add cheese, whisking until melted and well combined. Add half of the pasta water to help come together. Continue adding pasta water one tbsp at a time until melted and thick sauce forms.
Add pasta shells and broccoli to sauce and stir until combined. Add additional pasta water if needed. Serve hot.