Cut meat into 4 serving pieces. Season pieces with salt and pepper.
In a large sauté pan, heat olive oil on medium-high until it shimmers.
Add meat; brown about 3 minutes on both sides and remove from the
pan. Lower heat to medium, add onions and mushrooms and cook slowly
for about 4 minutes, or until the onions are translucent. Add garlic,
capers and oregano and cook 1 minute more.
Raise heat to medium-high and pour the sherry into the pan to loosen
juices that stick to the pan during cooking. Bring sherry to a boil,
add marinara sauce to the pan and simmer uncovered for about 5 minutes,
or until sauce is thickened. Return beef to the pan and heat thoroughly.
Serve over mashed potatoes (recipe for garlic mashed potatoes follows).
Mound potatoes on platter, pour marinara over and then top with
Marinara Sauce: Combine ingredients in small saucepan. Bring to
a boil, then lower heat and simmer gently, uncovered, 10 minutes.
Leftover tomato paste can be frozen. Place in ice cube tray in 1-
or 2-tablespoon amounts. When frozen, pop out and freeze in plastic
bag or container suitable for freezer.
Garlic Mashed Potatoes: Boil potatoes, garlic and 1 teaspoon salt in enough water to cover
the potatoes. Drain, reserving water if you prefer. Remove garlic
cloves and discard. Smash potatoes, butter and milk together with
a large fork until fluffy. The dish should not be smooth and creamy
- you want a thick, homey texture. Otherwise, the marinara sauce
will merge with the potatoes, making a runny mess. Season to taste
with remaining salt.