Preheat oven to 200°C (390°F). Place walnuts on a small baking sheet and bake in the oven for about 5 minutes, just until fragrant. Remove from the oven and let cool.
In a small bowl, mash two bananas with a fork. Add 2 tablespoons of maple syrup and stir until incorporated. In another bowl, whisk together the ricotta and 1 tablespoon of maple syrup, set aside.
On a floured working surface, stretch out (or roll out) the dough into a 28-cm (11-inch) round (or similar). Transfer to a greased tart pan (or cookie sheet or pizza stone; whichever you have on hand).
Brush dough with butter. Evenly spread ricotta mixture all over. Top with an even layer of mashed bananas.
Slice the remaining two bananas, either vertically or into small rounds. Place sliced bananas on the pizza, brush all with remaining butter.
Put pizza in the oven and increase the oven temperature to 220°C (425°F). Bake for 20 minutes, until the dough is golden brown and crisp, the bananas are tender and very fragrant.
Meanwhile, beat the cream until it forms hard peaks (either with a hand mixer, stand mixer or by hand). Roughly chop the toasted walnuts.
Remove pizza from the oven and let cool for 5 minutes before you remove it from the pan. Sprinkle pizza with walnuts and cut into equal slices. Serve with a side of whipped cream.