Preheat oven to 350 Fahrenheit
Lay both dried chilies on a baking sheet and roast for 6-8 minute, until chilies become aromatic and darken in color. It is ok that the two types of chilies get mixed together. Allow chilies to cool.
Break each chili open and shake out most of the seeds. Remove stems if they are present. Discard the seeds and stems.
Take half of the cleaned chilies, combine with the 1/2 tsp Sichuan peppercorns and grind into a fine powder. Set aside
Take the other half of the dry chilies and grind into a coarser powder.
Place the course chili powder into a metal heatproof bowl or pot and combine with the sesame seeds. Set this aside for later.
Put the rapeseed oil into a medium-sized pot and heat up to 450 Fahrenheit. There should be plenty of extra space in the pot because the hot oil will bubble up when the aromatics are added. Oil should be smoking at this point.
Turn off the heat, allow the oil to cool for a minute or two and then add the onions, scallion, ginger, cinnamon, black cardamom, star anise and bay leaves to the pot, all at once. Be careful, the oil will aggressively bubble up at first but will then subside.
Once ingredients are in, turn heat back on to medium and allow aromatics to gently fry in the oil until they turn golden brown, about 8 minutes
Strain the oil into another pot, pressing on the solids to extract as much oil as possible. Discard the solids.
Bring the infused oil up to 400 Fahrenheit
Very carefully pour approximately HALF of the hot oil over the coarse ground chili powder/sesame seed mix from earlier. The oil should sizzle and bubble as this is happening. Stir with a metal spoon.
After about 1 minute, add the finely ground chili flakes (which contain the Sichuan pepper) to the bowl.
Bring the rest of the oil back up to 400 Fahrenheit if it cooled down. Pour it over the finely ground chili in the same manner as before. Stir well.
Allow oil to rest at room temperature until cool. Once cool, you may use the oil but it will get better after a day or two.
Store in an airtight container in the fridge for up to 2 months.