Be careful not to overwork the dough or the biscuits will be tough.
Combine olive oil, shallots, tomatoes and brown sugar in a bowl. Cook for 15 to 20 minutes in a sauté pan over medium heat. Stir very gently with wooden spoon a few times to prevent burning but to keep tomatoes plump, avoid over stirring. If moisture evaporates too quickly just put a lid on the pan. Remove from heat and cool completely.
Preheat oven to 375 degrees F. Line a baking sheet with parchment paper.
Combine the flour, cornmeal, baking powder, baking soda, salt, pepper and rosemary in a food processor. Pulse until blended. Add the cold butter pieces. Pulse until mixture just resembles coarse meal.
Transfer mixture to a bowl. Stir in buttermilk and the tomato and shallot mixture until mixture just comes together. Start with adding 3/4 buttermilk, depending on the moisture of the tomatoes you may have to add more buttermilk.
Turn onto a lightly floured surface and gently knead until dough holds together. Do not overwork the dough or the biscuit will be tough. Wrap in parchment or waxed paper. Chill for 30 minutes.
Roll dough on a lightly floured surface to a thickness of ½-inch. Use a round 2 1/4-inch cookie cutter to cut 10 to 12 biscuits. Brush biscuits with beaten egg. Bake 15 to 17 minutes or until golden.