This is how I make homemade french fries too,instead of double frying them,I cook them first,then fry them crisp.
You can add onions & bell peppers,I prefer them this way.
Scrub potatoes clean. Chop into 1-inch cubes. Place potatoes in a large saucepan, cover with water and cook over medium-high heat for 15 minutes. Drain,dry well, transfer to a rimmed baking sheet. Drizzle with oil and drop small pieces of butter throughout. Sprinkle with salt and pepper. Toss lightly, bake for 30 minutes, tossing every 15 minutes. Reduce oven to 400 degrees, toss potatoes and cook for an additional 15 minutes. Top with green onions.Serve immediately.