Preheat the oven 400 degrees F. In a mixing bowl, dissolve the yeast in the water. Add 3 tablespoons of the olive oil, rosemary, garlic, flour, salt and cheese. Mix and knead well by hand until you have a smooth ball of dough. Place the dough in a greased bowl and cover with a damp cloth. Let the dough rise until double in size, about 1 hour. Turn the dough out onto a floured surface and punch down. Divide the dough into 4 pieces. Round each piece of dough. Using your fingers, flatten each round of dough, very thin. Brush each round with olive oil and sprinkle with cheese and kosher salt. Place the dough on a parchment lined baking sheet and bake for 10 minutes. Remove from the oven. Spread both sides of the bread with the horseradish mayonnaise. Layer the beef, cheese, red onions and tomatoes, in-between the bread. Place on a platter and serve with potato chips.
Yield: 4 individual flatbreads