All kinds of pastry should be baked in a moderately hot oven, for a high temperature is necessary to expand the air or gas, and thus make the pastry light, and also to burst the grains of the flour, thereby enabling these to absorb the fat immediately it melts. Unless the heat is sufficiently great to act upon the flour in this manner, the melted fat runs out and leaves the paste less rich, and also, probably, both heavy and tough. An oven with a good bottom heat is desirable for baking tarts and tartlets; when heated from above it is advisable to bake, or partially bake, the tarts before filling them.