Pre-heat your oven to 170 degrees Celsius. Grease and line an 8" square, metal cake tin with foil/ parchment/ butter paper2.
Melt the butter3 in a saucepan over a low flame.
Turn the heat off and add both the brown and regular sugar to the butter; stir well so that the sugars melt completely and form a golden butterscotch liquid4. Here’s a before and after picture of the sugars being mixed into the melted butter.
Sift the flour and baking powder directly into the saucepan. Stir well to ensure there are no lumps. The mixture will get to a semi-solid dough like consistency at this point, which is fine. Here’s what it will look like:
Beat two eggs until the whites and yolks are well mixed; you can add a tsp of vanilla essence to the eggs while beating, though this is not essential. Add the beaten eggs to the saucepan and stir well. The mix will now get back to a batter state. Here’s a before and after picture of mixing the eggs in:
Add 6 tsps of rum at this point; most of it is going to cook off in the oven and you’ll notice a barely-there rum taste in the final product. Add 2 – 3 tsps more if you want a noticeable, strong, rum flavor.
Fold the walnuts and raisins into the batter with a spatula or wooden spoon.
Pour the batter into the lined tin and bake for 25 – 30 mins.
I recommend baking for 25 mins at first, then checking if the blondies are cooked through by inserting a tooth-pick or skewer into the middle. The skewer should come out clean if they are done. If not, bake for an additional 5 mins. When done, the top of the cake should be a light golden colour, while the edges should turn a deeper golden brown, and be crisp! Here’s what it should look like:
Remove from the oven and allow to cool in the tin for about 20 mins. Run a knife around the edges, to make sure it separates from the walls of the tin. Turn the tin over onto a rack/ plate and allow it to release. Flip the blondie slab back onto a cutting board and slice into 16 even sized, squares. You now have a batch of Rum & Raisin blondies to eat warm or store in an airtight container for later5.