1. Preheat the oven to 350°F.
2. Line a baking sheet with parchment paper.
3. Place small mounds of shredded sharp cheddar cheese on the baking sheet, about 2 inches apart.
4. Flatten each mound slightly into circles.
5. Bake for 8-10 minutes until the cheese is melted and golden.
6. Remove from the oven and let the cheese cool slightly but remain flexible.
7. Carefully lift each cheese circle and press it into the cups of a muffin tin to create a cup shape.
8. Allow the cheddar cups to cool completely in the muffin tin, then remove.
9. Prepare the avocado feta mousse by blending 2 avocados, 1/2 cup crumbled feta cheese, 1 tablespoon lime juice, 6 tablespoons milk, and 1/4 teaspoon black pepper until smooth.
10. Store the mousse with plastic wrap pressed directly onto its surface to prevent browning, if making ahead.
11. For the crispy kale topping, tear kale leaves into small pieces and toss them with olive oil, red pepper flakes, and a pinch of salt.
12. Bake the kale at 350°F for about 8-10 minutes until crispy.
13. Let the crispy kale cool completely.
14. When ready to assemble, spoon or pipe the mousse into the cheddar cups.
15. Top each cup with a small piece of crispy kale.
16. Serve immediately and enjoy!