Baking milo biscuits for the first time

My recipe for milo biscuits

Ingredients:

1. 227g butter

2. 240g self raising flour

3. 25g corn flour

4. 100g milo powder (from tin/refill pack)

5. 2 tablespoon brown sugar

6. 1 egg

7. 25g milk powder

Steps:

1. Preheat the oven at 140 degrees celsius.

2. Cream the butter  and milo together for 3 mins under slow speed. Be careful the powder will fly everywhere

3. Add in the beaten egg.

4. Add in sugar.

5. Add in the sifted flour, milk powder and corn flour and stir with spatula to combine

6. Put on baking tray lined with parchment/baking paper.

7. Bake for 40mins under 140 degrees. Baking time varies depending on your oven make.

8. Take out and leave tray to cool on cooling rack.

9. Store in air tight container. 

Note: this recipe can bake 2 trays of cookies depending on your oven size. 

Optional: add in chocolate chips.

I was wondering if I should let it bake longer or increase temp since inside still a bit uncooked. Or perhaps just make v thin layer so it can cook properly.