Cook the bacon until crisp, then drain on paper towels and crumble it into small pieces. Reserve 1/4 cup (about 30 g) for mixing into the batter and keep the remaining 1/4 cup (about 55 g) for topping.

Place the cold mashed potatoes in a large bowl. Add the eggs, sour cream, flour, garlic powder, salt, and black pepper. Stir until evenly combined.

Fold in 3/4 cup (85 g) of the cheddar, 1/3 cup (35 g) sliced green onions, and 1/4 cup (about 30 g) crumbled bacon. Mix just until the ingredients are distributed. The mixture should be thick enough to scoop and hold its shape.

If the potato mixture looks very loose or spreads immediately when scooped, add another 1 tablespoon (8 g) flour and mix gently. Avoid adding too much flour because it can make the waffles dense.

Let the potato mixture stand for 10 minutes. This gives the flour time to absorb some moisture and makes the mixture easier to portion.

Preheat a Belgian-style or deep-pocket waffle maker according to the manufacturer's instructions. Lightly grease the plates with butter or oil if needed.

Place about 1/2 cup (120 ml) of the mixture into the center of the waffle iron. Spread it gently toward the edges without pressing it completely flat. Avoid overfilling, as the mixture can expand slightly and squeeze out.

Close the waffle maker and cook for about 4 to 6 minutes, or until the potato waffle is deeply golden brown and releases easily from the plates. If it sticks, give it another 30 to 60 seconds before trying again.

Transfer each finished waffle to a wire rack: Do not stack hot waffles, because trapped steam can soften the browned exterior.

Repeat with the remaining potato mixture, lightly greasing the plates between batches if necessary.

Top the hot waffles with the remaining 1/4 cup (28 g) cheddar and let it melt from the residual heat. Finish with the reserved bacon and green onions, plus optional sour cream.

Serve the waffles immediately while the edges are crisp and the cheese is warm and melted.