- In a large bowl, add burger patty ingredients. Mix by hand to ensure everything is combined, but not packed together.
- Divide into 4, 4-ounce balls and refrigerate, covered for an hour.
- To make radish pickles: Heat water and whisk in sugar and salt. Add vinegar and radishes. Set aside.
- To make dressing: Reserve half the apple cider vinegar and half the extra virgin olive oil and set aside. Add remaining ingredients to standing blender or immersion blender. Blend and with blender running, slowly pour in remaining oil and vinegar. Toss thinly sliced fennel with 3 tablespoons of dressing.
- To cook burgers: Shape each round into a patty shape with a slight dimple in the center. Heat a grill pan, or your outdoor grill to high and brush lightly with a neutral oil. Cook each side about 5 minutes, or until the internal temperature reaches 160˚ F.
- To build burgers: Layer radicchio or little gem lettuce, carrot, burger patty, fennel slaw, and gorgonzola.