Preheat the Oven:
Preheat your oven to 180°C/350°F (standard) or 160°C/320°F (fan-forced). Prepare a 12-hole standard muffin tin by brushing it generously with the garlic butter mixture.
Prepare the Butter and Garlic:
In a microwave-safe bowl, melt the butter with the crushed garlic in 30-second bursts. Stir until combined. Use some of this garlic butter to brush the muffin tin, ensuring to coat each hole generously. Reserve the remaining garlic butter for later.
Mix the Dry Ingredients:
In a large bowl, whisk together the plain flour, baking powder, baking soda, and salt until well combined.
Mix the Wet Ingredients:
In a separate bowl, whisk together the lightly beaten egg, milk, sour cream, vegetable oil, chopped parsley, and crushed garlic.
Combine Wet and Dry Ingredients:
Pour the wet ingredients into the bowl with the dry ingredients. Mix gently, about 8 times, until just combined. Add the grated cheddar cheese and mix as few times as possible, just until any remaining bits of flour are incorporated (no more than 7 big stirs). The secret to soft muffins is not overmixing.
Fill the Muffin Tin:
Divide the batter evenly between 11 muffin holes. The batter should be thick and fill the muffin tin to the top. If the batter forms a ball shape due to using a scooper, leave it as is.
Bake the Muffins:
Bake for 22-25 minutes, or until the muffins are golden, crusty, and spring back when touched in the center.
Finish with Garlic Butter:
Remove the muffins from the oven and transfer them to a cooling rack. Brush the tops with the reserved garlic butter (microwave it again if needed). Let the muffins cool slightly before serving.