Patatas Bravas

For Potatoes:

4 cups (1-inch) cubed peeled baking potatoes (about 1 1/2 pounds)
1 Tablespoon butter
2 teaspoons olive oil
1/2 teaspoon kosher salt
1/4 teaspoon red pepper flakes
2 garlic cloves, minched

For Sauce:

1 teaspoon olive oil
1 cup diced onion
1 cup diced green bell pepper
1/4 (or more) teaspoon kosher salt
1/4 teaspoon red pepper flakes
1 8 ounce can tomato sauce
2 Tablespoons tomato paste

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 6-8 minutes or until browned, stirring frequently. 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, tomato sauce and tomato paste; 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.