Cook the Bacon: Place a large, non-stick frying pan over a medium heat. Add the streaky bacon and cook for 6-8 minutes, turning occasionally, until golden and crispy. Transfer the bacon to a plate lined with kitchen paper and set aside. Carefully wipe the excess fat from the pan.

Prepare the Bread: While the bacon is cooking, lay out the four slices of sourdough. Mix your grated cheddar and Monterey Jack cheeses together in a small bowl. Spread the softened butter evenly over one side of each slice of bread.

Fry the Eggs: In a separate small frying pan over a medium-low heat, crack in the two eggs. Cook for 3-4 minutes, or until the whites are set but the yolks are still runny and jammy. A sprinkle of black pepper on top is a nice touch.

Assemble the Sandwich: Place two slices of bread butter-side-down in your large frying pan (off the heat for now). Spread a tablespoon of tomato relish on each slice. Top with half of the cheese mixture, then arrange three rashers of crispy bacon on each.

Add the Egg: Gently place a fried egg on top of the bacon on each sandwich. Sprinkle the remaining cheese over the eggs. I find that covering the egg completely with cheese helps hold everything together as it melts.

Grill the First Side: Place the remaining two slices of bread on top, butter-side-up. Turn the heat to medium-low. Cook for 4-5 minutes, pressing down gently with a spatula, until the bottom is a deep golden brown and the cheese has begun to melt.

Flip and Finish: Carefully flip the sandwiches over using a wide spatula. Cook for another 4-5 minutes on the other side, until it's equally golden and crisp, and the cheese is fully melted and gooey.

Rest and Serve: Transfer the breakfast grilled cheese sandwiches to a cutting board and let them rest for a minute. This helps the cheese set slightly so it doesn't all spill out. Slice in half diagonally and serve immediately.