Preheat the oven to 200°C. Lightly grease a rectangular 29cm x 21cm oven tray. Mix the flour, salt, basil and paprika into a large bowl. Soak the baking soda in a little buttermilk and set aside until needed. Stir in the buttermilk and baking soda mixture, and just enough of the rest of the buttermilk to form soft dough. Turn out onto a lightly floured board. Roll out into a rectangle of 1cm thick. Spread with tapenade and scatter over Mediterranean mix and thyme leaves. Roll up from one long side to form a log. Slice the log into sections of about 3cm each and place, sliced side up, next to one another in the oven tray. For the glaze, mix the yolk and water. Brush over the bread. Bake for 15 minutes, then reduce the temperature to 170ºC and bake for a further 5 to 10 minutes.