Place the dry ingredients in a mixing bowl and whisk to mix. Set aside. I suggest not using an electric mixer. Use a rubber spatula to mash the softened butter. Then add both sugar and mix until combined. Add room temperature egg (for egg version) or yogurt (for eggless version) and mix until combined. Add red bean paste and mix to combine
Add the dry ingredients and food coloring (if using). Use a spatula to fold to combine. Don't overwork the dough, just mix until you don't see any more loose flour. The dough will be very sticky at this point. Do not be tempted to add more flour
Cover the cookie dough and let it chill in the fridge for at least 4 hours or overnight is best if you have the time
Shape the cookies:
Preheat oven at 350 F (180 C). When the oven is done preheating, scoop about 1 1/2 Tbsp (30 grams) of the cookie dough out. The dough is still sticky but easier to handle because it's cold. Spray your palms with some non-stick cooking spray or coat lightly with a bit of oil. Roll it into a round ball and place them on a lined cookie sheet
Roll each one in granulated sugar first and then generously roll them in icing sugar. This step prevents the icing sugar from being absorbed by the dough and you won't get the crinkle effect. Roll them 2 more times in icing sugar to make sure each ball is well-coated or the confectioners' sugar will not show much after baking
Put the baking sheet into the oven, 3rd rack from the top. Let them bake for 12-13 minutes for crisp on the edge and soft center. This yield soft chewy cookies. They will still appear to be very soft at the center when you pull them out from the oven. Let them cool on the baking sheet for 5 minutes then transfer to a cooling rack. They will firm up a bit as they cool down.
If you use margarine, the cookies will spread out more and thinner and hence, crispier in texture.