Lightly grease a 10 x 4-inch loaf pan. Melt 2 tablespoons of the butter in a heavy frying pan and sauté the onion until it is soft and light golden. Set aside to cool.

Sift the flour into a large bowl and stir in the yeast, mustard, salt and pepper. Stir in three-quarters of the grated cheese and the onion. Make a well in the center. Add the milk and water; blend to a soft dough. Turn out onto a lightly floured surface and knead for 10 minutes, until smooth and elastic.

Place the dough in a lightly oiled bowl, cover with lightly oiled plastic wrap and let rise, in a warm place, for 45 - 60 minutes or until doubled in bulk.

Turn the dough out onto a lightly floured surface, punch down, and knead gently. Divide into 20 equal pieces and shape into small rounds. Place half in the prepared pan and brush with some melted butter. Top with the remaining rounds of dough and brush with the remaining butter.

Cover with oiled plastic wrap and let rise for 45 minutes, until the dough reaches the top of the pan. Meanwhile, preheat the oven to 375°F.

Sprinkle the remaining cheese on the top. Bake for 40 - 45 minutes or until risen and golden brown. Cool on a wire rack.