Heat the oven to 250°C (230°C fan) on the grill setting. Cut two 4cm pieces from the green tops of the spring onion and reserve them for the salad and garnish. Slice the remaining spring onion into thin rings. Wash the potatoes and grate them coarsely.
Heat a small ovenproof pan on medium heat. Add the bacon slices and fry for ca. 2min. per side until golden and crisp. Take them out of the pan and and pat with a paper towel to remove excess oil. Roughly chop the bacon into bits. If desired, reserve any bacon fat that was in the pan. Wipe out any burnt residue in the pan.
Heat 2Tbsp olive oil or the bacon fat on medium heat. Add the sliced spring onions and fry for ca. 1min. to soften. Then stir in the potatoes, a large pinch of salt and pepper and 3Tbsp water. Reduce the heat to medium-low. Cover and cook the potatoes for 12–15min. until softened but still holding their shape. Stir regularly to prevent burning. Add more water if it sticks to the bottom of the pan.
Turn the heat to low. Mix in the bacon and cheese, until the cheese is melted and it all comes together into a soft mass. Be sure to scrape the bottom of the pan. Scoop the mixture onto a piece of baking paper. Slide the baking paper with the mixture on top, back into the pan. The paper will be in between the pan and the frico. Flatten the frico into the base of the pan.
Grill ca. 7min. in the oven's center rack until the top is crisp and golden. Then carefully flip the frico by first sliding it onto a plate. Place a baking paper and a plate on top. Invert it onto the top plate, so the crisp side faces down. Remove the top plate and paper. Slide the frico back into the pan crisp side down. Grill again ca. 7min. until the top side is crisp and golden.
In a large bowl, mix together ½Tbsp olive oil, 1Tbsp balsamic vinegar, ½ the basil cream and a pinch of salt, pepper, and sugar. Cut the tomatoes into wedges and toss in the dressing. Slice the reserved spring onion into thin lengthwise strips. Stir some into the salad and use some to garnish the frico. Remove the frico from the pan, cut into wedges and serve warm with the salad alongside.