Preheat the oven to 375 degrees F.
To make the basil spread, wash the basil and remove the leaves from the stems. In a blender, add the basil leaves and a generous helping of salt and pepper. Then pour in olive oil until the blender is filled one-fifth of the way. Blend for 30 seconds. (The olive oil will help facilitate the blending, so don't be shy about adding more olive oil to help your blender blend the basil leaves into a smooth paste.) Pour the basil spread into a bowl. Set aside.
To make the olive topping, chop the kalamata olives as finely as possible and put in a small bowl. Add a drizzle of olive oil. Stir.
Next, cut up your tomatoes and mozzarella.
Lastly, cut your bread into 1/2-inch-thick slices, at a diagonal. Spread slices of bread on a baking sheet and drizzle with more olive oil. Sprinkle a little salt on all the pieces and put in the oven until crispy, 10 to 15 minutes.
Move the toasted bread onto a serving platter. Add the toppings and spreads in any combination; they all work great! For example: mozzarella, basil spread and tomatoes; olive topping and mozzarella; mozzarella and prosciutto, to name a few. Serve.
Crostini are perfect for gatherings and parties of any size. You can prep many toppings and serve whenever you want by toasting more bread. Typically, crostini are crunchy toasts, but if you like softer bread as your base, remove the bread from the oven sooner.