Warm the milk to a lukewarm temperature (about 30 degrees Celsius). In a bowl, place the yeast (fresh or dry), half of the sugar, 2 tablespoons of flour, and the milk. Mix thoroughly and beat until the ingredients are combined. Cover with a cloth and set aside the starter for about 20 minutes in a warm place, such as an oven preheated to 35 degrees Celsius (put it in the turned-off oven). After this time, the starter should begin to foam and bubble. If the yeast is working properly, proceed to the next steps.

Melt 25 g of butter (save the rest for the crumble) and allow it to cool. In a bowl, place: 80 g of flour, 40 g of sweetener (save the rest of the flour and sweetener for the crumble), melted butter, the rest of the sugar, and a pinch of salt. Mix together.

Add the starter and crack in the egg. Mix and beat with a spoon until a smooth, lump-free mass is obtained. Leave the dough in the bowl – cover with a cloth and set aside in a warm place to rise, such as an oven preheated to 35 degrees Celsius (put it in the turned-off oven).

After about 30-60 minutes, when the dough has increased in volume, transfer it to a small baking pan lined with baking paper. Set the dough aside for a moment to rise a little more. In a bowl, mix the remaining flour, sweetener, and butter. Mix and beat until a crumbly texture is formed. If necessary, add a little water or flour to achieve the right consistency (crumbly). Spread the low-sugar jam (such as blueberry, orange, strawberry, or another) over the dough and sprinkle with the crumble. Place in an oven preheated to 180 degrees Celsius and bake until properly cooked through and browned, about 40-50 minutes. If the crumble browns too much, reduce the temperature slightly.

Eat warm or cold. Store the yeast bun in an airtight container (or wrapped, e.g., in plastic wrap) in the refrigerator for up to 4-5 days.