Brush a 6-hole jumbo muffin tin with oil and preheat the oven to 200°C.
In a large bowl sift together the flour, baking powder, salt, sugar, mustard powder, and dried thyme.
Mix in the grated cheddar and the grated parmesan cheese, reserving a little of each to top the muffins.
In a jug, whisk together the milk, oil, water, and eggs.
Make a well in the center of the dry ingredients and add the wet ingredients. Mix them together with a wooden spoon until just combined. Do not overmix.
Spoon the muffin batter into the prepared muffin tin and top with the reserved grated cheese.
Bake in a preheated oven for about 25 minutes or until a toothpick inserted into the center of the muffin comes out clean.
Allow the muffins to cool slightly on a wire rack before serving, enjoy!