To prepare potatoes, place potato in a medium saucepan; cover with water. Bring to a boil. Cook 1 minute or until crisp-tender; drain well.
Heat a large nonstick skillet over medium-high heat. Add butter and 2 teaspoons oil to pan, swirling to coat bottom of pan; heat 30 seconds or until foam subsides. Add potato to pan; sauté 8 minutes or until browned, stirring twice. Stir in 1/4 teaspoon salt, 1/8 teaspoon red pepper, and garlic; sauté 1 minute. Remove potato mixture from pan; keep warm.
To prepare sauce, heat pan over medium-high heat. Add 1 teaspoon oil to pan, swirling to coat; heat 15 seconds. Add onion and bell pepper; sauté 5 minutes or until tender, stirring frequently. Add 1/4 teaspoon salt, 1/8 teaspoon red pepper, and tomato sauce; bring to a simmer. Cook 1 minute. Pour onion mixture into a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Serve sauce with potato mixture. Garnish with parsley sprigs, if desired.
If you like fiery food, use one-fourth to one-half teaspoon red pepper in the sauce. For the crispest potatoes, stir only every two or three minutes; frequent stirring can damage them.