Melt butter in a heavy-bottom saucepan. Add onions and carrots and cook until tender, about 5 minutes. Whisk in flour and cook 5 more minutes. Add broth and continue stirring as mixture thickens. Add broccoli and simmer over medium heat until tender, 20 to 25 minutes, stirring occasionally. Remove from heat and cool to room temperature.
Place cooled soup into the 48-ounce XL Multi-Serve Nutri Ninja. PULSE until smooth, using long pulses.
Remove the blades from the cup after blending.
Transfer soup back to saucepan. Simmer until heated through, then whisk in milk and cheese and season to taste with salt and pepper.
Go ahead, embrace your inner meal prepper. We hear you, making smoothies the night before is a huge time saver. But, heads up, never store your smoothies with the blade assembly attached—active ingredients in some foods may lead to pressure buildup and possible injury. Store them with Sip & Seal™ Lids instead.
NOTE: Always allow the soup to cool to room temperature before blending. Once blended, transfer mixture back to a saucepan and heat to desired temperature.