Grease and line the bottom and sides of the cake tin. Preheat the oven to 180C/160C fan. Melt the butter and chocolate in a large glass bowl over a small saucepan of simmering water - making sure the bowl isn’t touching the water.
Meanwhile, put the sugar and eggs into a mixing bowl and use an electric whisk for a few minutes until very light and fluffy. When the butter and chocolate has melted, stir them together until smooth then pour it into the egg mixture. Gently fold the mixture together, trying not to knock air out of the beaten egg mixture, until it’s just combined. Sieve the flour over the mixture, add the chocolate chips, then carry on folding very gently, again until it’s all just about mixed together.
Pour half of the mix into the prepared tin and use a spatula or palette knife to spread it around. Loosen the jam in a warm saucepan, if necessary, then gently spoon it over the blondie batter and spread it around with a palette knife. Carefully spoon in the rest of the batter, trying to keep the jam layer as level as possible - then smooth it over. Arrange the jammy dodgers on top, and poke them in with your finger so they’re half submerged. Bake for 25 minutes, until a the top has crusted and the middle is still slightly wobbly. If it looks very wobbly then cook for another 5 minutes.
Leave to cool fully in the tin then cut into 16 squares. Eat immediately or store in an airtight tin for up to three days.