In the bowl of an upright mixer fitted with a dough hook attachment combine the flour, bicarbonate of soda, and one teaspoon of salt. Add the butter and mix on low speed until incorporated, about two minutes.
With the machine still running, slowly add the water until the mixture forms a dough around the hook. Transfer the dough to a lightly floured work surface and knead for five minutes until smooth.
Cut the dough into four equal pieces. Form into disc shapes and wrap in plastic wrap. Refrigerate for 30 minutes.
Place a grill pan over medium-high heat or preheat a gas or charcoal grill. On a lightly plain floured work surface, roll out each piece of dough into an 20-25cm circle, about 3mm thick. Brush each circle with the extra-virgin olive oil and grill for four minutes each side. Remove the flatbread from the grill to cool slightly.
In a small bowl combine the ricotta cheese and lemon zest and season to taste with salt and pepper. Divide the mixture between theflatbreads and sprinkle with the fontina cheese. Arrange the prosciutto slices on top of the cheeses.
To serve cut each piadina into 8 wedges and transfer to a serving platter. Garnish with the chopped basil.