Cook the leeks in butter for 10 minutes. Set aside and let cool.
Place 2 layers of paper towels on a plate. Arrange the bacon slices on top, then cover with 2 more layers of paper towels.
Cook in the microwave for 4 to 6 minutes, at maximum intensity, checking every 2 minutes, or until the bacon is crispy.
Let cool, then chop the bacon.
In a bowl, combine the flour and baking powder.
Add the leeks, bacon, and grated cheddar cheese.
Preheat the oven to 350 F (180 C). Prepare a cake pan by greasing it generously if it’s a metal pan, or not at all if it’s a silicone or parchment-lined pan.
In another bowl, beat the eggs with the walnut oil and buttermilk.
Add the egg mixture to the flour mixture until it’s homogeneous.
Pour the mixture into the prepared pan and bake for 50 minutes, or until a wooden skewer inserted in the center comes out clean.
Let cool before unmolding and slicing.
Serve with a green salad.