Cut the baguette into 1/2 inch thick slices, diagonally to maximize the surface area of the bread slices. Toast the baguette slices in a panini grill for 10 minutes, or bake them in a 350ºF preheated oven for 5 minutes. Optionally, grill them for a minute or two just to get the grill marks on them.
Wash the nectarines and slice them into 1/4 inch thick wedges.
Mix Mascarpone cheese with honey and lemon juice in a bowl.
Once the baguette slices are finished toasting and have cooled down a bit, spread 2 Tbsp of the Mascarpone spread on each of the baguette slices. Then, top the crostini with nectarine slices. Drizzle with honey. Serve at room temperature.