Step 1Trim ends, then cut each head of radicchio into lengthwise quarters and then into crosswise ribbons about 1/4 -inch wide. Combine the radicchio in a cold skillet with 3 tablespoons olive oil, garlic, salt and balsamic vinegar. Cover and cook over medium-low heat, stirring occasionally, until the radicchio has softened, about 10 minutes.
Step 2Reduce the heat to low and cook until the radicchio is quite soft and the bitterness has cooked out, about 5 minutes more. Season to taste with salt and perhaps just a little more balsamic vinegar. Remove from heat and set aside. Remove the garlic before serving.
Step 3Slice the baguette into 1/2 -inch slices and toast until lightly browned on both sides.
Step 4Spoon a heaping teaspoon of the radicchio marmalade onto each slice of bread and top with a similarly sized spoonful of burrata (try to get both the filling and the wrapping in each spoonful). Sprinkle each with a light grinding of black pepper and a drizzle of the remaining olive oil and serve.