In a small pot combine farro, stock concentrate, and 2½ cups water. Bring to a boil and cook, stirring occasionally, until tender, 25-30 minutes. TIP: If you end up with any excess stock, pour it out. Or, if stock evaporates before farro is done, add a splash of water.
Meanwhile, trim and thinly slice radishes. Dice tomato. Zest and quarter lime.
Rub corn all over with a drizzle of olive oil. Heat a large pan over medium-high heat. Add corn and cook, rotating frequently, until some kernels are charred, 7-9 minutes. Turn off heat; transfer to a cutting board to cool slightly. Wipe out pan.
Heat same pan over medium heat. Add pepitas, 2 tsp water, 1 tsp sugar, and a pinch of chipotle powder and salt. Cook, stirring, until pepitas are coated and lightly browned, 2-3 minutes. Transfer to a small bowl.
Squeeze juice from half the lime into a large bowl. Whisk in sour cream, 1 tbsp olive oil, half the lime zest, ¼ tsp chipotle powder, and ½ tsp sugar. Add water, 1 tsp at a time, until mixture reaches a drizzling consistency. Season with salt.
Stir 1 tbsp butter, remaining lime zest, salt, and pepper into farro; divide between bowls. Slice corn kernels off cob; discard cob. Add corn, arugula, tomato, pepitas, and as many radishes as you like to bowl with dressing. Toss to combine. Season generously with salt. Top farro with arugula mixture and cheese. Serve with remaining lime wedges on the side.