Preheat oven to 200°C (180°C fan forced). Use non-stick spray or butter to grease muffin tray (or use cupcake liners)
Combine self-raising flour, cinnamon and salt in medium sized bowl
In a large bowl, cream butter and sugar using electric mixer on high speed until light and fluffy (around 2-3mins).
Add eggs, plain yogurt/sour cream, and vanilla essence. Mix on medium speed until combined.
Add dry ingredients to wet ingredients and fold until just combined. Add expresso and mix until it forms a thick, smooth mixture. Don’t over mix.
Using a large spoon, share batter evenly between cases. Sprinkle brown sugar over muffins. Bake for 5 mins on 200°C (180°C fan forced) before reducing temperature to 180° (160°C). Bake for 15 - 17 more mins, or until golden brown. To determine if baked well: if you tap on the top of the muffins they should bounce back, and a skewer inserted in them should come out clean.
Serve warm or room temp... best if they are fresh out of the oven! Optional: serve with salted caramel drizzled on top