Preheat the oven to 500°F (if using a baking sheet) or as high as it will go (if using a baking stone/steel; place the stone/steel in the bottom third of the oven before you start preheating). Let the oven preheat for at least 30 minutes. Then, if you’re using a baking stone or steel, switch the oven to Broil on high.
Put the sliced leek in a colander and rinse it thoroughly under cold running water, using your fingertips to separate the layers. Drain well, then transfer the leek slices to a paper towel–lined plate and blot them dry.
In a medium skillet over medium heat, cook the bacon until it just begins to brown at the edges, 5 to 7 minutes. Remove the skillet from the heat and transfer the bacon to a paper towel–lined plate to drain. Pour the bacon grease into a small ramekin for brushing the dough.
Stretch or roll out your dough to a 12- to 14-inch circle, then transfer it to a baking sheet / pizza pan or a lightly floured pizza peel (if using a baking stone/steel).
Use a pastry brush to spread a very thin layer of bacon grease all over the dough. Scatter the sliced leeks and cooked bacon on top, then sprinkle with the cheese. Drizzle the toppings with half of the heavy cream.
Transfer the pizza to the oven and bake until the crust is golden around the edges and evenly browned on the bottom—8 to 10 minutes on the baking sheet, 6 to 8 minutes on the baking stone/steel.
Remove the pizza from the oven and immediately drizzle the remaining heavy cream over top. Wait 3 to 5 minutes for the cream to congeal, then slice and serve.