Ripe tomato shells are filled with a chive and cheese mixture, then baked

6 large ripe tomatoes
1/4 tsp. kosher salt
1/4 tsp. ground black pepper
2 Tbs. butter
2 Tbs. all-purpose flour
3/4 C. milk
1/4 tsp. dry mustard
1/2 C. sharp cheddar cheese
1/2 C. chives
3 egg whites

Cut 1/2-inch from the top of each tomato scoop out seeds and core. Sprinkle the inside of shells with salt and pepper invert onto paper towels to drain. Heat butter in a small pan, over a medium to melt. Whisk in the flour until bubbly. Now gradually whisk in the milk. Heat while stirring, until the mixture is thickened. Stir in mustard, cheese, and chives. Mix well and continue to heat and stir until the cheese melts. Remove from heat and allow to cool slightly. Gently fold in the egg whites. Spoon into the drained tomato shells set into a greased baking pan bake at 400 degrees F for 15-18 minutes, until tops are lightly browned. Remove from oven and serve hot