No Fail Red Velvet Cupcakes - 1st attempt

Remembered the first time I had red velvet cupcakes, I thought it was made of cherry (by looking at the colour). From then on, I would choose the red velvet one whenever there were assortment of cupcakes in front of me.
Only recently when I wanted to make some for myself then I realized they are made of chocolate powder and red coloring. I was so wrong. Haha!
I was looking for easy to make and use only 1-2 eggs recipe and this is what I tried. I must say this is a no fail recipe, even though I use whisk instead of electric mixer and I mixed up some steps, the end result was still promising and satisfying-- fluffy and cottony and I liked it!
(below method is my version, see here for original recipe)

Ingredients: (make 7 cupcakes)
60g unsalted butter, room temperature (I used Margarine)
150gm caster sugar (I used 90-100gm)
1 egg
10g cocoa powder
20ml red coloring
1/2 tsp vanilla essence
120ml buttermilk (I used 100ml low fat milk with 1/2 tsp White vinegar, rest for 5 min or more)
1 & 1/2 tsp white vinegar
150gm plain flour (I used cake flour, sifted)
1/2 tsp salt (I omitted as I use margarine and not unsalted butter)
1/2 tsp baking soda

Method:
1. Preheat oven to 170 deg C.
2. Whisk margarine and sugar till slightly pale, creamy and light.
3. Add egg in and mix well.
4. In a separate bowl, mix together cocoa powder, red coloring, vanilla essence and some milk. Whisk till well mixed and no lumps.
5. Add to butter mixture and mix evenly and well colored.
6. Add remaining milk and alternate with cake flour. Mix till everything well incorporated.
7. Add baking soda and vinegar(and salt if you use unsalted butter), continue to stir till well mixed.
8. Fill each cup 3/4 full and bake in preheated oven for 25-30min.
9. Check if skewer inserted in centre come out clear. Once clear, remove from oven and cool on rack.

I am submitting this post to very good recipes-My valentine challenge.