Brew iced coffee: Brew the coffee then refrigerate to cool.

Preheat oven: Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or grease the muffin cups with cooking spray.

Prepare crumble topping: In a small bowl, combine the flour, oats, brown sugar, and melted butter for the crumble topping. Mix until crumbly and set aside.

Mix dry ingredients for the muffins: In a large mixing bowl, combine the oats, flour, brown sugar, baking powder, baking soda, and salt.

Mix wet ingredients: In another bowl, whisk together the milk, melted butter, egg, and vanilla extract until well combined.

Combine wet and dry ingredients: Pour the wet ingredients into the dry ingredients and stir until just combined. It’s OK if there are lumps. Do not overmix.

Fill muffin cups: Divide the muffin batter evenly among the prepared muffin cups, filling each about 3/4 full.

Add crumble topping: Sprinkle the crumble topping evenly over the muffin batter in each cup.

Bake muffins: Bake in the preheated oven for 18 - 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Prepare clementines: While the muffins are baking, peel and segment the clementines.

Pour the cooled coffee over ice. Prepare to your liking.

Serve: Serve the oatmeal muffins alongside the clementine segments and iced coffee.