Whisk yeast in water until smooth, mix with flour, oil and salt and knead with the dough attachment of the electric hand mixer to a smooth elastic dough. If necessary, add extra water or flour. Let rise, covered, in a warm place for 45 minutes.
Knead dough on a lightly floured surface and roll out. Butter baking sheet with 1 tablespoon of butter and line with the dough, making an edge all around.
Cut bacon into small pieces. Peel and dice onions. Heat remaining butter in a pan and saute onions and bacon for a few minutes. Season with salt and pepper, add cream and spread evenly over the dough.
Bake in preheated oven at 180°C (approximately 350°F) for about 35 minutes. Turn off oven temperature and let cake stand for 5 minutes in the oven. Remove from the oven and serve warm.