The dietician recommended Calcium fortified Oatly to us when we were weaning. We grew out of the intolerance, but my memories are:
Breakfasts
toast! vary the breads tho - crumpets are usually milk free. Also english muffins.
Or Normal porridge oats, made up with water and fruit purées / jam / raisins, or made up with oatly.
Puddings
I enjoy cooking, so these may not appeal
Birds custard powder (in the TIN - not the packets), made up with oatly, and no sugar. Add cocoa powder for chocolate custard, or bananas, or other fruit.
I also made up Jelly with oatly as the liquid.
Home made cake, as you've discovered! If you make them up as fairy cakes, then freeze them, they defrost very well.
Crumbles / fruit pies. With Custard!
Bananas cook very well - either wrapped in foil, and put in the oven (still in skins), even better if you split the skin and stuff a row of chocolate buttons in, but not sure how dairy free chocolate melts, or sliced and fried in butter, brown sugar and cinnamon.
Krispie cakes - melt butter substitute and syrup, stir in cocoa and icing sugar. Mix with rice krispies (or cornflakes, or crushed shredded wheat), and put in small cake cases.
Hope that gets you started. If your prepared to cook and freeze, lots of normal puddings can be made with dairy free alternatives.
Good luck - we struggled to get enough calories in my LO, so were always adding sugar, fat and oils (e.g. avocado, oily fish) to meals!