In bowl or food processor, combine flour, baking powder, baking soda and salt. Using pastry cutter or on/off pulse motion, cut in butter until butter is the size of peas with a few larger pieces. Pour buttermilk over, tossing with fork or pulsing, until the dough JUST comes together, adding one tablespoon more buttermilk if required. Knead lightly into disc. Cover with plastic wrap and refrigerate for at least 30 minutes or for up to three days.

Meanwhile, place tomato slices on paper towel to soak up any extra liquid.

In bowl, toss together breadcrumbs, garlic, thyme, basil, and pepper.

On lightly floured surface, roll out pastry to roughly 12-inch circle. Transfer to parchment paper lined rimless baking sheet. Leaving two-inch border, sprinkle half of breadcrumb mixture over dough. Arrange tomato slices, slightly overlapping, on top of breadcrumbs. Sprinkle with Asiago, Parmesan and then remaining breadcrumb mixture. Lift pastry over filling, pleating and folding pastry as necessary and using beaten egg to “glue” pleats together.

Brush egg all over pastry. Bake in centre of preheated 400 degree Fahrenheit oven for about 25 to 30 minutes or until galette is golden brown. Let cool for 10 minutes Serve warm.