Heat the oven to 375°F with a rack in the middle. Line an 8 1/2 × 4 1/2-inch metal loaf pan with parchment rated for this temperature, covering the bottom and long sides with an overhang. Leave the pan ungreased. Gather a food processor, flexible spatula, kitchen scale and instant-read thermometer before handling the eggs.

Measure 480 g of rinsed, thoroughly drained Great Northern beans. Spread them briefly on a clean towel and blot away visible surface water without squeezing them dry. Put the beans and 150 g eggs into the processor. Process until the mixture looks like a thick, mostly smooth puree, stopping to scrape the bowl so whole beans do not remain underneath the blade.

Add 150 g oat flour and pulse just until evenly incorporated. Scrape down the sides and fold through any dry pockets with the spatula. The mixture should be a thick, scoopable batter that holds soft ridges, rather than a pourable liquid or kneadable dough. Do not taste the raw batter. Wash hands and food-contact equipment after handling raw eggs.

Transfer the batter directly to the prepared pan. Press it gently into the corners and smooth the surface to an even thickness. Keep the center level rather than building a tall mound. There is no bench rest or proofing; move the filled pan straight into the heated oven.

Bake for 55 minutes, checking at 45 minutes. The surface should feel firm, and a thermometer inserted into the center should register 195°F. If the center remains cooler or visibly wet, continue baking until it reaches that target and is set. A skewer may carry moist crumbs but should not emerge coated in wet batter.

Cool in the pan for 15 minutes, then lift out and cool on a wire rack for 45 minutes. Cut into 10 slices, making 5 servings of 2 slices. Refrigerate promptly after cooling. In surroundings above 90°F, finish cooling in the refrigerator to meet the shorter safe-storage deadline.