Preheat the oven to 425°F.
Toss the diced russet potatoes with the olive oil, 1/2 teaspoon Kosher salt, and 1/4 teaspoon black pepper.
Spread onto a parchment-lined baking sheet in an even layer. Roast for 25–30 minutes, stirring halfway through, until golden brown, crisp around the edges, and tender.
While the potatoes roast, cook the bacon, if needed, and shred the cheddar cheese.
Whisk together the eggs, milk (if using), the remaining 1/2 teaspoon kosher salt, and the remaining 1/4 teaspoon black pepper.
Melt the butter in a large nonstick skillet over medium-low heat. Pour in the eggs and gently stir until just set and still slightly glossy, about 4-5 minutes. Remove from the heat, the eggs will continue cooking slightly from the residual heat.
Warm the flour tortillas for 15–20 seconds in the microwave or briefly in a dry skillet. This makes them easier to roll without tearing.
Divide the fillings evenly among the tortillas.
Fold in the sides of each tortilla, then roll tightly into a burrito. Serve immediately or place the burritos seam-side down in a dry skillet over medium heat for 1–2 minutes per side, until lightly golden.