- No need to preheat the oven yet, the dough needs to chill! 
- Place flours, cocoa powder, bicarb, salt and chocolate chips into a medium sized bowl and stir until all of the chocolate chips are coated in flour. Leave to one side. 
- Place butter and sugars into a large bowl, or the bowl of your stand mixer, and beat on medium-high speed until light and fluffy, 2-3 minutes. 
- Add in the eggs and vanilla, scraping sides as necessary and mix until well combined, around 45 seconds. 
- Add in the vinegar and mix briefly to combine. 
- Add in food colouring, a little at a time, until you reach desired colour. You want it to be bright red, but you can always add in a little more after you've mixed in the flour. 
- Tip in the flour/chocolate mix and mix on low until a soft dough forms. If unhappy with the colour, add a little more and then mix until well incorporated. 
- Once you are happy with the colour of your dough, tip into a medium sized bowl and cover with cling film. Place in the fridge for at least 6 hours, overnight if possible. 
- Once chilled, preheat the oven to 180C/350F and line 2-3 baking trays with a silicone mat/grease proof paper/a Silpat etc. 
- Using a 1.5tbsp cookie scoop, scoop balls of dough and place 2 inches apart on your lined baking trays. Press down ever so slightly on the balls, so they don't roll away. 
- Place in the oven for 8-10 minutes, until set around the edges, but still soft and under baked in the middle. The outer edges will look matte, the middle still soft and squidgy. 
- Leave to cool on baking trays completely. Once cool, flip half of the cookies upside down so the flat base is facing upwards, then place 1 tsp of chocolate spread onto half of the Red Velvet cookies and spread into an even layer, right to the outer edges of the cookie. 
- Sprinkle each half covered in spread with heart shaped sprinkles, if desired, and then top with the remaining cookies. 
- Red Velvet Sandwich Cookies will keep in an airtight container, at room temperature for 5 days.