Step 1

Pierce sweetpotatoes and apples with fork tines. Microwave sweetpotatoes and apple on high until apple is very tender, about 6 to 7 minutes. Remove apple; set aside until cool enough to handle.

Step 2

Continue microwaving sweet potatoes on high until tender, about 4 to 5 minutes longer. Set aside until cool enough to handle.

Step 3

Meanwhile, in large saucepan over medium heat, heat oil. Add onion and curry powder. Cook and stir until onion begins to brown, about 5 minutes.

Step 4

Add broth. Bring to a boil, reduce heat to low; simmer 5 minutes.

Step 5

Transfer broth mixture to bowl of food processor; reserve saucepan.

Step 6

Halve sweetpotatoes and apple. Remove apple core, scoop potato and apple pulp from skin. Add to processor. Add salt; whirl until very smooth, gradually adding apple juice through processor feed tube. Transfer mixture to reserved saucepan.

Step 7

Bring to boil over medium heat; whisk in yogurt. Reheat just until hot (do not boil).

Step 8

Serve topped with croutons, if desired.